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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.

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Perhaps I should have called this thread, "newbies read this first"
Or system design basics
Great information, but I'm wondering about the air calculations. One of the functions of the grow bed is to infuse the pond water with oxygen as it passes through, via the agitation of passing through the media as well as from the plants- is there no way to quantify how much oxygen we get from a gallon (or square foot) of grow bed? Seems that this would be an important Design Number, especially for folks like me who are interested in reducing energy consumption and using intermittent flood and drain cycles.

I also want to add that my drain is a 1/2" drain, with a 1" in-flow pipe, and sized smaller purposefully to allow just a few minutes more soak time (around 10 minutes). The timer is set precisely to stop well short of overflow, but there is also a 1-1/2" back-up drain, in case the pump refuses to shut off or smalll drain gets clogged.
I'm not sure how to go about quantifying the aeration provided by a flood and drain grow bed.

However you make a point that I want to add an important reminder to. Plants only give off oxygen while the sun is shining, at night plants take up oxygen and give off CO2 the same as the fish and bacteria. (important note if you have lots of algae as it can leave fish gasping at the surface of the water before dawn if bad enough.)

Anyway, I know grow beds provide ample aeration for their own purposes (the bio-filter, the plants, and the break down of solids withing them.) But they may not always provide ample aeration to the fish tank especially if the system is heavily stocked and the water warm as in summer. When you start adding in very intermittent cycling of the pump to the grow beds (such as leaving the pump off all night long), I think it becomes even more necessary to add aeration to the system.
Now this is not to say that a system can't run without supplemental aeration, I know of many systems that have managed it but there are risks and I know of people who have had disasters because of it.

Just because certain types of fish can survive very low oxygen levels, that does not mean they can also grow fast while subjected to low oxygen levels. By adding extra air to a tank, I saw a marked improvement to my tilapia feeding rate. I'm kinda trying to say that cutting down on pumping and air, you might be seeing a false economy since it could mean that it will take you twice as long to see the same increase in fish mass. So it will depend on what your goals and requirements are with a system to know what economies are worth the trouble. If you cut your electric usage in half but it takes you twice as long to grow out the same amount of fish, have you really saved anything?
TCLynx said:
I'm not sure how to go about quantifying the aeration provided by a flood and drain grow bed.

However you make a point that I want to add an important reminder to. Plants only give off oxygen while the sun is shining, at night plants take up oxygen and give off CO2 the same as the fish and bacteria. (important note if you have lots of algae as it can leave fish gasping at the surface of the water before dawn if bad enough.)

...snip...

That's a good reminder- I admit to not really thinking about that. But it does seem to indicate that leaving the system off over night (half the night in my case) is not such a bad thing, as long as the fish load is light. Since I have more of an aesthetic fish pond with a low fish-to-gallon ratio, as opposed to a food rearing tank with a high fish-to-gallon ratio, oxygen is not much of an issue.

I just caught four 10" tilapia and 6 mollys (two pregnant) out of a stream in Hilo today. That's my current fish load. The koi have eluded me for two days straight!

So- your points are valid and reflect a great amount of experience in aquaponics and I thank you. Looking forward to learning even more! -- Shawn
Shawn,

I'm going to politely disagree with you on the aeration, but that's because my fish are my priority and the plants are just a nice bonus :)

I prefer to over aerate my water because my plant to want water ratio is high, and because we experience blackouts more frequently than I'd like. Should anything happen, I'd like to know that my fish are going to be okay. I have plenty of seeds to plant, and my plants can make more seeds, but my fish are much harder (and more expensive) to replace. So, I guess it would depend on your priorities and what's readily available.
I don't think we disagree at all- that is the correct approach for your system- it all depends on your system's needs. My needs are totally different. For my previous system, (also a desktop) I had a bubbler to keep the fish healthy no matter what. Aquaponics formulas are designed with maximum efficiency in mind- the most fish and plants produced period, with little regard for the amount of energy used. If you just want to have a lovely little pondscape attached to a grow bed, or use less energy, then the formulas change. When I get around to setting up a fish tank for serious food rearing, you can bet I'll be tossing in lots of tiny bubbles!

Emma Lysyk said:
Shawn,

I'm going to politely disagree with you on the aeration, but that's because my fish are my priority and the plants are just a nice bonus :)

I prefer to over aerate my water because my plant to want water ratio is high, and because we experience blackouts more frequently than I'd like. Should anything happen, I'd like to know that my fish are going to be okay. I have plenty of seeds to plant, and my plants can make more seeds, but my fish are much harder (and more expensive) to replace. So, I guess it would depend on your priorities and what's readily available.
Yes, it does all come down to design goals.

If you want to save a lot on enegry or don't want to give much space to filtration or whatever, then the fish numbers will definitely have to be reduced.

There are things that a highly stocked system can do to be more energy efficient but there are limits.
Just a question on the numbers in the OP. It said to stock a 300 gall tank and media system with roughly 60 fish. 300 gallons is 40 cubic feet. I thought I (as a complete newbie) was supposed to stock at 1 fish per cubic foot...

My plan right now is a 8'x3'X4' (720 gallon )FT with two 7' X 4' X1' grow beds (roughly works out to 60 cubic feet/450 gallons). I want to do a CHOP pump in the sump set up. Is my math correct that I will need about a 300 gallon sump and that I can stock ___ number of fish? (60? 80?)

I know I have more water than I need, I'm planning that in hopes of a more stable system chemically and thermally. One big concern is that I'm in Phoenix, and I can foresee the heat could be a big problem even with shade, not so much for the tilapia, but I'm not sure how well plants will grow being bathed with 95+ degree water.... thoughts?
You are right that recommended stocking for a new system would be 1 fish (intended for 1 lb grow out) per cubic foot of flood and drain grow bed media.

The number 60 is actually a MAX stocking which once you have enough experience to handle that, you won't necessarily need some one telling you what you can handle. When I originally started this discussion I was still tending to use the max numbers when discussing system design. I have since switched over to the more reasonable recommended numbers.

For a system with 60 cubic feet of flood and drain grow bed media, start out stocking with 60 small fish that you intend to grow out to 1 lb (if growing something like catfish, you might want fewer if you want to grow them big or just harvest some small to make room for the others to get bigger. They are quite edible over a very wide range of sizes.)

Yes, more water makes for more stability. Add extra aeration then the heat is up and a bit of extra shade over the plant beds as well as the fish tank can help with heat. Being in a dryer climate, you will probably be able to manage a bit of evaporative cooling and things will likely cool off more at night there. It was quite hot here for several weeks and it was still cool enough that my catfish have been surviving fine. Tilapia can take the heat just as well as the cats can. Even with the extreme heat, I don't think I've ever experienced water much more than 95 coming out of the grow beds and going into a sump tank it will mix and cool off some before going into the fish tank.
What, no one has numbers for raft systems?
Look for.........FriendlyAquaponics on August 31, 2010 at 10:12pm
http://aquaponicscommunity.com/group/commercialaquaponics/forum/top...

If the link doesn't work....you'll have to join the 'group'...Friendly Aquaponics Talks Story and then read through...Aquaponics System Aeration and Water Flow Requirements




Kate Mink said:
What, no one has numbers for raft systems?
Thanks for starting this discussion, TC. While I agree with your stocking densities I think maybe they can be stated by the simple rules of going with a 1:1 up to a 1:2 fish tank volume to grow bed volume ratio (the later probably requiring that sump tank you mentioned), with 1 lb of fish for every 5 gallons of tank water with a mature bio-filter, and 1 fish per 5 gallons for startups. Make sense?

I'd like to start gathering up some of these generally accepted rules onto a page that we put up in the top left box of the home page as the third bullet. If no one objects I will start with those above for media based systems...along with the need for 12" or more of media depth. Sound good? Ideas for what we should call it?

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