A Community and Forum For Aquaponic Gardeners
Design numbers
So how many fish can I have in my 300 gallon tank? or how much Raft do I need to support 60 lb of fish? This is the place to share the numbers for designing a well balanced system.
I know the numbers for Flood and drain media so that is what I will share and I'll let the experts on rafts share that info.
Standard rule for media systems is (Actually this is MAX and only for the skilled fish keeper.)
3 kg of fish per 100 liters of flood and drain media (those fish can be living in 50-100 liters of water, and a sump tank could be necessary to provide extra water if the fish tank is on the small side of the numbers) So to convert that to measure that we think in more commonly.
5 lb of fish per 25 gallons of flood and drain media.
A more appropriate recommendation for fish stocking would be 20-25 fish (500 gram grow out) per 500 liters of grow bed or 1 fish per cubic foot of grow bed with a planned grow out of 1 lb. Total grow bed and fish tank should be of equal volume or if a sump tank or indexing valve is used there can be more grow beds than fish tank up to twice as much grow bed as fish tank.
Perhaps this might be a little conservative but it is better to start light on fish while cycling up a new system. Once you get comfortable you can decided how best to keep the fish.
A big note here. Those fish weights are for the planned final grown out weight of fish in a system.
Example, say you have a 300 gallon tank and 300 gallons of flood and drain media filled grow bed.
Say it's a simple system pumping from the fish tank to the grow beds which drain back to the fish tank. Say you are growing tilapia and you plan to grow them out to 1 lb if you can.
I would say stock only about 60 fish. (I'm not into planning on lots of fish deaths so I would only personally pad this number by a few fish-I would not personally stock 100 fish and plan on loosing 40.) Again this is assuming that you will grow all those fish out to eating size in that same tank. Again these numbers are a bit skewed, Kinda figuring people would start eating their tilapia a bit smaller than a pound to make enough room for the other fish to get to a pound. Also, tilapia tend to allow people to pull off higher numbers than are really possible with most other types of fish. In such a 300 gallon 1:1 system I am currently growing only 30 catfish.
They start small in a new system and give you time for the bio-filter to cycle up to the load.
Some other handy numbers for figuring out pump sizing and aeration.
You want your water pump to cycle the equivalent of the volume of you fish tank each hour at the amount of head you are requiring of it. So for that 300 gallon system, if you run the pump continuously and use auto siphons to drain the grow bed, you need a pump that will do about 400 or 500 gallons an hour. If you wish to use a timer and flood all the beds together 15 minutes per hour, you need a pump that will move that 400-500 gallon in15 minutes so you need a pump that can do 1600-2000 gallons per hour. Another option is an aquaponic indexing valve where you could pump for a period of time to each bed in sequence. Figuring out the pump required for this will depend on the indexing valve chosen and the timer one wishes to use.
On pumps, do some extra research, a cheap pump often uses more electricity so it may cost more in the long run than the costly pump. Always look for performance curves to tell how much flow can be expected at different head heights. Remember that small plumbing will reduce efficiency, never restrict your pump output.
On to air pumps. This will definitely be different than the DWC system since for a media system, you only need to aerate fish tanks/sump tanks. Aeration of tanks helps keep solids moving along and not collecting in with the fish. Aeration will also assist the fish in being able to metabolize food and grow faster. If there is not enough oxygen, fish don't eat as well. Highly aerated water also assists the bacteria where ever they may form to convert ammonia and nitrite to nitrate. It also assists in keeping the water circulated to avoid dead spots and brings bottom water up to the surface for better aeration in that way (it isn't just the bubbles contact with water that aerates.)
Aeration numbers. Simple rules of thumb I've been told.
You want 1 cubic foot per minute of air for each 400 gallons of fish tank. You need 1 psi to push air though the air stone and 1 psi to push air down 28 inches under water. So for the average system you want to figure out how much air an air pump will provide at 2 psi and then figure out how many cubic feet per minute you need to provide for your system volume.
I have a 60 watt air pump that provides 2 CFM at 2 psi. That air pump runs all the time. Normally it runs on mains power but I have installed a relay so that if mains power goes out, I have a deep cycle battery that will keep the air running to my system for at least a day. (So there is aeration and backup all in one air pump plus the appropriate batter, charger, inverter and a DTDP relay.)
Air I'm sure is a completely different story in Raft culture and I've heard of raft systems being run almost completely on air with minimal water pumping. But I know almost nothing about blowers so I'll leave that explanation to others.
Some notes about plumbing. Gravity drains always need far larger plumbing than their pumped counterparts. For example. If you are pumping into a tank using 1" plumbing, you had better make sure your gravity drains and overflows out of that tank are far larger than the 1" inlet or the tank will overflow. Don't make your overflows too close to the rim of the tank or they might not have a chance to work before the tank actually overflows over the top. You need enough fall or height for many gravity drains to work, it might not have to be a lot but you can't drain uphill by gravity. So if you are gravity draining from a fish tank, make sure the place to which the water drains to is lower than the high water level in the fish tank or it won't work.
If in doubt about plumbing, go bigger. It is easy to reduce down later if you need to but if the hole or bulkhead is too small, it can be difficult to up-size later.
I know the numbers for Flood and drain media so that is what I will share and I'll let the experts on rafts share that info.
Standard rule for media systems is (Actually this is MAX and only for the skilled fish keeper.)
3 kg of fish per 100 liters of flood and drain media (those fish can be living in 50-100 liters of water, and a sump tank could be necessary to provide extra water if the fish tank is on the small side of the numbers) So to convert that to measure that we think in more commonly.
5 lb of fish per 25 gallons of flood and drain media.
A more appropriate recommendation for fish stocking would be 20-25 fish (500 gram grow out) per 500 liters of grow bed or 1 fish per cubic foot of grow bed with a planned grow out of 1 lb. Total grow bed and fish tank should be of equal volume or if a sump tank or indexing valve is used there can be more grow beds than fish tank up to twice as much grow bed as fish tank.
Perhaps this might be a little conservative but it is better to start light on fish while cycling up a new system. Once you get comfortable you can decided how best to keep the fish.
A big note here. Those fish weights are for the planned final grown out weight of fish in a system.
Example, say you have a 300 gallon tank and 300 gallons of flood and drain media filled grow bed.
Say it's a simple system pumping from the fish tank to the grow beds which drain back to the fish tank. Say you are growing tilapia and you plan to grow them out to 1 lb if you can.
I would say stock only about 60 fish. (I'm not into planning on lots of fish deaths so I would only personally pad this number by a few fish-I would not personally stock 100 fish and plan on loosing 40.) Again this is assuming that you will grow all those fish out to eating size in that same tank. Again these numbers are a bit skewed, Kinda figuring people would start eating their tilapia a bit smaller than a pound to make enough room for the other fish to get to a pound. Also, tilapia tend to allow people to pull off higher numbers than are really possible with most other types of fish. In such a 300 gallon 1:1 system I am currently growing only 30 catfish.
They start small in a new system and give you time for the bio-filter to cycle up to the load.
Some other handy numbers for figuring out pump sizing and aeration.
You want your water pump to cycle the equivalent of the volume of you fish tank each hour at the amount of head you are requiring of it. So for that 300 gallon system, if you run the pump continuously and use auto siphons to drain the grow bed, you need a pump that will do about 400 or 500 gallons an hour. If you wish to use a timer and flood all the beds together 15 minutes per hour, you need a pump that will move that 400-500 gallon in15 minutes so you need a pump that can do 1600-2000 gallons per hour. Another option is an aquaponic indexing valve where you could pump for a period of time to each bed in sequence. Figuring out the pump required for this will depend on the indexing valve chosen and the timer one wishes to use.
On pumps, do some extra research, a cheap pump often uses more electricity so it may cost more in the long run than the costly pump. Always look for performance curves to tell how much flow can be expected at different head heights. Remember that small plumbing will reduce efficiency, never restrict your pump output.
On to air pumps. This will definitely be different than the DWC system since for a media system, you only need to aerate fish tanks/sump tanks. Aeration of tanks helps keep solids moving along and not collecting in with the fish. Aeration will also assist the fish in being able to metabolize food and grow faster. If there is not enough oxygen, fish don't eat as well. Highly aerated water also assists the bacteria where ever they may form to convert ammonia and nitrite to nitrate. It also assists in keeping the water circulated to avoid dead spots and brings bottom water up to the surface for better aeration in that way (it isn't just the bubbles contact with water that aerates.)
Aeration numbers. Simple rules of thumb I've been told.
You want 1 cubic foot per minute of air for each 400 gallons of fish tank. You need 1 psi to push air though the air stone and 1 psi to push air down 28 inches under water. So for the average system you want to figure out how much air an air pump will provide at 2 psi and then figure out how many cubic feet per minute you need to provide for your system volume.
I have a 60 watt air pump that provides 2 CFM at 2 psi. That air pump runs all the time. Normally it runs on mains power but I have installed a relay so that if mains power goes out, I have a deep cycle battery that will keep the air running to my system for at least a day. (So there is aeration and backup all in one air pump plus the appropriate batter, charger, inverter and a DTDP relay.)
Air I'm sure is a completely different story in Raft culture and I've heard of raft systems being run almost completely on air with minimal water pumping. But I know almost nothing about blowers so I'll leave that explanation to others.
Some notes about plumbing. Gravity drains always need far larger plumbing than their pumped counterparts. For example. If you are pumping into a tank using 1" plumbing, you had better make sure your gravity drains and overflows out of that tank are far larger than the 1" inlet or the tank will overflow. Don't make your overflows too close to the rim of the tank or they might not have a chance to work before the tank actually overflows over the top. You need enough fall or height for many gravity drains to work, it might not have to be a lot but you can't drain uphill by gravity. So if you are gravity draining from a fish tank, make sure the place to which the water drains to is lower than the high water level in the fish tank or it won't work.
If in doubt about plumbing, go bigger. It is easy to reduce down later if you need to but if the hole or bulkhead is too small, it can be difficult to up-size later.
Replies to This Discussion
-
Permalink Reply by Kate Mink on
-
Imperial or American? The gallons aren't the same. I don't see a units note in the spreadsheet I downloaded from your Imperial calculator link.
RupertofOZ said:I'm sure both Joel and Murray will no doubt comment shortly...
But Dr Wilson Lennard has just released an "backyard aquaponics system sizing tool"....
You can download both the modeling spread sheet, as well as the "how to" explanatory notes, right now.
The metric calculator (excel) :
http://www.backyardaquaponics.com/Travis/Aquaponic%20media%20bed%20...
The imperial Calculator (U.S.) (excel) :
http://www.backyardaquaponics.com/Travis/Aquaponic%20media%20bed%20...
The How to notes (pdf):
http://www.backyardaquaponics.com/Travis/Aquaponic%20media%20bed%20...
You can visit Wilson Lennards website here http://www.aquaponic.com.au/backyard.htm
You'll also find the links on Murray's forum site as well.....
So what are you waiting for, download the modeling calculator and see how your systems stacks up to the scientific recommendations.
Sylvia Bernstein said:I'll try to get a Simple Rules of Thumb for Media Based Home systems up on the home page by the end of the week, along with some verbiage at the beginning about that this is for beginners, and encouraging the reader to delve into the rest of the discussions to learn the whys behind the rules, the variations to the rules, and the deeper ideas that are contained therein. I'll also send them to Friendly's website for their system, Travis's website for Barrellponics, and the UVI website for their info. I'll leave the comments section up for a week or so so members can comment. Sound like a reasonable plan?
-
Permalink Reply by TCLynx on
-
This tool has also made it over to the BYAP site as well.
Seems that in their solids calculations, worms are not taken into account. So perhaps the fact that my system actually functions at all, might be at least partially due to the hand full of worms I added to each bed as I started them up.
I find it interesting that the tool says I need more square footage to take care of the solids than I need plants to take care of the nutrients while my experience with my system with worms in it seems to push the other way around. I'm gonna test out a big raft bed to see if adding more plant square footage will get my nutrient levels down though heading into winter without a greenhouse will probably slow feeding to the point that nutrients will be down anyway.
-
Permalink Reply by Darryl Hinson on
-
Hello All:
I'm looking for a solution or tip on how to gain some confidence with my barrel system....my barrels are, of course, curved at the bottom and my siphon cover pipe is flat....i could round it out but that doesnt seem like a good fix....one of my barrel fills up and runs over the top..(plenty of water coming in)....and when I push down on the cover pipe, the siphon will start.....it seems to be leaking at the bottom....not air...but it's not sealing and not allowing a negative pressure to build in the top of my cover tube......no rocks or any obstructions down in the pipe.
I have a washer down there.....any suggestions..for amyone....I know there are a few barrel systems out there...
Darryl
-
-
Siphons can be a bit of a challenge in barrels cut the long ways seeing as the varrying volume by height makes getting the flow rates perfectly balanced with the siphon even more challenging.
Sounds like you are trying a bell siphon. It also sounds as if you have an air lock at the bottom which is causing your bell to float up am I right? I've seen some people manage this problem by adding a brick to hold it in place or something of the sort but that might not be the right answer.
Anyway, perhaps your inner stand pipe is too tall if you are having one of the barrels overflowing.
some description of what happens with the drain pipe down below the barrels might help here.
You might also do a search for Affnan since he has done a modification to the basic bell siphon which seems to help many people get the siphons operating better over a wider range of inflows.
Anyway, if you can adjust your drain pipes so the water has an easier time pushing the air down the pipe rather than causing it to float up, you might have a better chance of getting your siphons to start without intervention. Having the bottoms drain freely rather than having a closed small pipe going up and down causing air locks will probably help.
There is a link to a Useful Diagrams thread on my Group page which may have some helpful pictures for you.
Look for Useful Diagrams Thread Link
Darryl Hinson said:Hello All:
I'm looking for a solution or tip on how to gain some confidence with my barrel system....my barrels are, of course, curved at the bottom and my siphon cover pipe is flat....i could round it out but that doesnt seem like a good fix....one of my barrel fills up and runs over the top..(plenty of water coming in)....and when I push down on the cover pipe, the siphon will start.....it seems to be leaking at the bottom....not air...but it's not sealing and not allowing a negative pressure to build in the top of my cover tube......no rocks or any obstructions down in the pipe.
I have a washer down there.....any suggestions..for amyone....I know there are a few barrel systems out there...
Darryl
-
-
thanks TC....I really dont know exactly where to go from here....My gravel is in the beds and its a pain to get to the siphon bottom....I might modify it a bit......I feel like this entire way of growing is uncharted waters.......I may be wrong but my take on this stuff at the backyard level is done by a bunch of do it yourselfers (me included) and a lot ot trial and error.....no 2 systems appear to be the same....unless I buy a ready made system, which I cant afford....so I'm dealing with barrels that I got for free and a bunch of pvc at the local hardware store.....and many hours on the internet trying NOT to reinvent the wheel....I thought I'd be a little farther down the road by now....not giving up though....
Darryl
-
Permalink Reply by RupertofOZ on
-
TCL, the capacity required for bio-filtration, nitrification, mineralisation and even oxygenation acheived through flood & drain... has always been greater than the nutrient requirment of plants...
And again, the tool is based on Wilson Lennards initial thesis work... without worms...
The extra mineralisation and breakdown of solids... with worms.... allows for increased plant production....
Coindidently, the degree of capacity for proper mineralisation and nitrification... translates into increased surface area for planting....
That's one of the reasons the whole arguement for shallow vs deeper grow beds... and/or grow beds becoming clogged... is a nonsense and myth.... unless qualified by increased surface area...
You can see the effect of this with the recent trend toward system that have doubled the stocking density of fish... and/or halved the suggested grow bed ratio to 1:1....
They always exist on a knife edge of filtration.... more particularly oxygenation... especially when temperatures, growth and feed rates are rising....
It's not uncommon to see such systems where both the stocking density has been doubled, and the ratio halved... with residual ammonia and nitrite readings... and high (relatively) nitrate readings... without the ability to address either situation...
IMO, and I've consistantly stated it ... 30 kg / 1000L is a maximum stocking rate... Tilapia are an exception.... with a 2:1 grow bed : fish tank ratio...
30kg/1000L... or more correctly 30kg/1000m3 ... is considered a medium/high stocking rate in RAS... and about the extent to which passive aeration methods can provide sufficient oxygenation for all system requirements...
Anything else... is a potential disaster waiting to happen...
The tool may not be perfect and worthy of five stars... and has some basic assumptions, well known in aquaculture, behind the formulas applied... but it is a good starting point... and deserves better than the one star rating you gave it....
P.S ... the tool, and evaluation of the BYAP kit systems utilising the tool... were listed on BYAP before any where else... although the latter may not have been publically released...
TCLynx said:This tool has also made it over to the BYAP site as well.
Seems that in their solids calculations, worms are not taken into account. So perhaps the fact that my system actually functions at all, might be at least partially due to the hand full of worms I added to each bed as I started them up.
I find it interesting that the tool says I need more square footage to take care of the solids than I need plants to take care of the nutrients while my experience with my system with worms in it seems to push the other way around. I'm gonna test out a big raft bed to see if adding more plant square footage will get my nutrient levels down though heading into winter without a greenhouse will probably slow feeding to the point that nutrients will be down anyway.
-
-
So using a grow bed less than 12 inches deep should not matter as long as you make the grow bed larger in length and width. For example having a grow bed that is 2ft wide x 4ft length and a 1ft deep would be the same as having a grow bed 2ft wide x 8ft length and 6inches deep, and could then allow for more plants
RupertofOZ said:TCL, the capacity required for bio-filtration, nitrification, mineralisation and even oxygenation acheived through flood & drain... has always been greater than the nutrient requirment of plants...
And again, the tool is based on Wilson Lennards initial thesis work... without worms...
The extra mineralisation and breakdown of solids... with worms.... allows for increased plant production....
Coindidently, the degree of capacity for proper mineralisation and nitrification... translates into increased surface area for planting....
That's one of the reasons the whole arguement for shallow vs deeper grow beds... and/or grow beds becoming clogged... is a nonsense and myth.... unless qualified by increased surface area...
You can see the effect of this with the recent trend toward system that have doubled the stocking density of fish... and/or halved the suggested grow bed ratio to 1:1....
They always exist on a knife edge of filtration.... more particularly oxygenation... especially when temperatures, growth and feed rates are rising....
It's not uncommon to see such systems where both the stocking density has been doubled, and the ratio halved... with residual ammonia and nitrite readings... and high (relatively) nitrate readings... without the ability to address either situation...
IMO, and I've consistantly stated it ... 30 kg / 1000L is a maximum stocking rate... Tilapia are an exception.... with a 2:1 grow bed : fish tank ratio...
30kg/1000L... or more correctly 30kg/1000m3 ... is considered a medium/high stocking rate in RAS... and about the extent to which passive aeration methods can provide sufficient oxygenation for all system requirements...
Anything else... is a potential disaster waiting to happen...
The tool may not be perfect and worthy of five stars... and has some basic assumptions, well known in aquaculture, behind the formulas applied... but it is a good starting point... and deserves better than the one star rating you gave it....
P.S ... the tool, and evaluation of the BYAP kit systems utilising the tool... were listed on BYAP before any where else... although the latter may not have been publically released...
TCLynx said:This tool has also made it over to the BYAP site as well.
Seems that in their solids calculations, worms are not taken into account. So perhaps the fact that my system actually functions at all, might be at least partially due to the hand full of worms I added to each bed as I started them up.
I find it interesting that the tool says I need more square footage to take care of the solids than I need plants to take care of the nutrients while my experience with my system with worms in it seems to push the other way around. I'm gonna test out a big raft bed to see if adding more plant square footage will get my nutrient levels down though heading into winter without a greenhouse will probably slow feeding to the point that nutrients will be down anyway.
-
-
Yep theoretically possible... but Kobus has already highlighted some of the "cons" ... like physical footprint...
If you were to elevate large area beds, there's also the cost... and the pysical limitation of accessability to harvest and plant...
More problematic is the question of root growth... where some plant types develope extensive root systems that in shallower beds can result in the flood level rising above the media level...
This is also likely to be true with a greater amount of plants in itself....
Also... a large shallow bed... IMO.... would require a distribution grid, rather than a singular water input...
The heating/cooling aspect of shallow beds that Kobus outlines... is a significant point to take into consideration... as is the possibility of increased evaporation...
Kobus Jooste said:While I remain a fan of not going too shallow (25 - 30 cm) on gravel beds due to the logistics and cost of building a big shallow one versus a deeper one, in theory, I see no problem with what you say. If you look at some rotating drum designs foor aquaculture, the media surface area is thin and extensive, while other designs are cylindrical. More than one way to skin a cat. You could get lots of heat gain / loss pout of a shallow extensive bed though. As long as you have the surface area and volume for nitrification and mineralization to take place, I think you have some leeway with how you package it. Look at DWC vs NFT. Plant roots in water taken to two extremes, and both works. From a system footprint, material cost and potential heat trap/sink point of view though, I see sense in the 12 inch deep bed theory. I must also admit that I am not 100% sure on the mineralisation effect that may be influenced by beds of different depths, only that to a certain decrease in depth, you will most likely decrease the risk of having an anoxic layer developing at the bottom of a bed over time.
Tony Tarantino said:
So using a grow bed less than 12 inches deep should not matter as long as you make the grow bed larger in length and width. For example having a grow bed that is 2ft wide x 4ft length and a 1ft deep would be the same as having a grow bed 2ft wide x 8ft length and 6inches deep, and could then allow for more plants
RupertofOZ said:TCL, the capacity required for bio-filtration, nitrification, mineralisation and even oxygenation acheived through flood & drain... has always been greater than the nutrient requirment of plants...
And again, the tool is based on Wilson Lennards initial thesis work... without worms...
The extra mineralisation and breakdown of solids... with worms.... allows for increased plant production....
Coindidently, the degree of capacity for proper mineralisation and nitrification... translates into increased surface area for planting....
That's one of the reasons the whole arguement for shallow vs deeper grow beds... and/or grow beds becoming clogged... is a nonsense and myth.... unless qualified by increased surface area...
You can see the effect of this with the recent trend toward system that have doubled the stocking density of fish... and/or halved the suggested grow bed ratio to 1:1....
They always exist on a knife edge of filtration.... more particularly oxygenation... especially when temperatures, growth and feed rates are rising....
It's not uncommon to see such systems where both the stocking density has been doubled, and the ratio halved... with residual ammonia and nitrite readings... and high (relatively) nitrate readings... without the ability to address either situation...
IMO, and I've consistantly stated it ... 30 kg / 1000L is a maximum stocking rate... Tilapia are an exception.... with a 2:1 grow bed : fish tank ratio...
30kg/1000L... or more correctly 30kg/1000m3 ... is considered a medium/high stocking rate in RAS... and about the extent to which passive aeration methods can provide sufficient oxygenation for all system requirements...
Anything else... is a potential disaster waiting to happen...
The tool may not be perfect and worthy of five stars... and has some basic assumptions, well known in aquaculture, behind the formulas applied... but it is a good starting point... and deserves better than the one star rating you gave it....
P.S ... the tool, and evaluation of the BYAP kit systems utilising the tool... were listed on BYAP before any where else... although the latter may not have been publically released...
TCLynx said:This tool has also made it over to the BYAP site as well.
Seems that in their solids calculations, worms are not taken into account. So perhaps the fact that my system actually functions at all, might be at least partially due to the hand full of worms I added to each bed as I started them up.
I find it interesting that the tool says I need more square footage to take care of the solids than I need plants to take care of the nutrients while my experience with my system with worms in it seems to push the other way around. I'm gonna test out a big raft bed to see if adding more plant square footage will get my nutrient levels down though heading into winter without a greenhouse will probably slow feeding to the point that nutrients will be down anyway.
-
-
As to the tool and the low rating. I'll admit, I'm not as fluent with metric and I therefore tested out the Imperial version. The lack of clarity (about which gallons are in use) and the notes being given in a mix of metric and imperial probably played a role in the low rating I gave it.
I can see where this would be a useful tool for designing more complex systems where you are keeping closer track of fish weight and exact feed % and I do like the redundancy when you are talking about systems where they are likely to push the limits.
Seeing as I'm not running with ammonia or nitrite levels showing, I don't think that I'm pushing the limits that much, I can shut off the air pump during hot weather and even after hours the dissolved oxygen levels were still fine in the fish tank. I would have expected to see the tool show that my system was at least close to reasonable. However, apparently since the 30 cm deep grow bed is the standard, that is the depth the tool applied and extrapolated that to square surface area instead of volume for the solids mineralization. I don't think that one was actually based on any trials of deep vs shallow grow beds, just the assumption that the mineralization mostly takes place the the top few inches based on soil studies.
Sorry, the tool needs some improvements, at least some clarification on the gallons used and the notes on the imperial tool should be converted to imperial to help it make more sense before I'm likely to give it a higher rating. My system is known to me in gallons so trying to convert that into metric and square meters just isn't that easy since most of my beds are not rectangular and they are mostly deeper than 30 cm.
-
-
Now over to the question of shallow grow beds.
I personally don't really recommend them for most situations.
I have done a 4' by 8' and 6 inch deep grow bed before. I found it very difficult to control the flood and drain of it using siphons. Just not enough leeway either side since siphons will normally leave a little water in the bottom of a bed and you want to leave the top inch or so of gravel dry, that doesn't give much space for rise and fall and makes it even easier for the siphon to suck air before it's time. It probably can be done with a siphon but I would advise larger media for it to keep the flow through the gravel faster.
Later I changed things around with that shallow bed and tied it in with the FLOUT of the neighboring bed. Since the neighboring bed was deeper, the shallow bed was able to drain down a little better with the "external flout" but the drain down was still hindered by constant inflow and the flow rate through the gravel.
If one were to feel compelled to use a shallow bed, then I would say follow Rupe's advice and use a distrobution grid and used timed flood and drain to feed the beds. I generally don't like these as they seem an excess use of materials that needs regular cleaning, however, I do have some beds that are getting a bit root bound because I planted huge bananas in them (they are still 12" deep in the center), for those beds, a distrobution grid might be needed to avoid the flooding over the gravel problem if I don't remove the banana plants (I promise I thought they were supposed to be dwarf!!!!! The catalog said 4' tall fruiting plants and the picture in the catalog showed something in a 3 gallon pot indoors! Apparently Aquaponics changes things.)
Anyway, my solution if one finds that deep grow beds are not growing enough plants to take care of the nitrogen, then it is pretty easy to add on some other means of growing plants to supplement the gravel. My system has some NFT pipes being fed water that was already filtered by the gravel beds, I also have some Zip grow towers running, I'm now in the process of adding a raft bed to see what I think of growing that way.
Now I will admit that currently I have about 350 gallons worth of barrel cut long ways type beds, these are 12" deep in the center and shallower to the outsides. Those beds get fed filtered water and are like timed flood and drain. I have 3 more even shallower beds, 7 inches deep that are fed a constant stream of filtered water and are constant flood growing water chestnuts and other water plants. This final use of a shallow bed I'm liking so far but still want to test out some different media for it.
-
-
Kate Mink said:Imperial or American? The gallons aren't the same. I don't see a units note in the spreadsheet I downloaded from your Imperial calculator link.
Through Sylvia I got the info that he was using US gallons for the imperial calculator.
- ‹ Previous
- 1
- 2
- 3
- 4
- Next ›
© 2024 Created by Sylvia Bernstein.
Powered by
