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So... I'm new to aquaponics but have quite a bit of experience in hydroponics. However, the question I have is something I havent found in my reading. I umderstand the general rule of stock density roughly being 5 gal - 10 per lb of grown out fish but that generally applies to growing traditional aquaponic crops, which are primarily light feeders. What if i had a media bed that ran tomatoes and peppers (heavy feeders), which would serve as biofiltration and could allow a much higher density of fish and then drain to a raft system with light feeders such as lettuce and basil and then return to the fish tank. My real question is, from an experienced aquaponics grower, can this b done? ...and how would i even begin to calculate the ratios.

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A study reported in the Journal of Plant Nutrition    Volume 16,  Issue 3,  1993 suggests that each kilogram increase in fish biomass can provide sufficient nutrient uptake for two tomato plants. 

 

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 "Mineral nutrient concentration and uptake by tomato irrigated with recirculating aquaculture water as influenced by quantity of fish waste products supplied            "

Ryan,

    You need enough bio-filtration for the fish load.  I'm not sure where you got 5 gal-10 lb of fish?  5 gallons of what? Your numbers actually sound a bit backwards to me.  I often do like 1-3 (depending on kind of fish) fish per 8-10 gallons of fish tank and I will have like 20 gallons of grow  bed to filter for it.  Now I tend to recommend light stocking densities and one should only figure they need more fish or nutrients if both of the following conditions are met.  1-the plants are showing signs of nitrate deficiency AND 2-the nitrate readings are 0.

I've found I can get away with a much lighter fish load even with some fairly heavy feeding plants provided the temperatures and aeration are right for the fish to be eating well.  That said, no matter what you still need the bio-filtration surface area to convert the fish wastes to plant nutrients.  Even if you have heavy feeder plants, if you don't have enough bio-filter, the ammonia and nitrite are going to kill your fish while the plants struggle.

Ya can't expect the plant roots to do all the filtration (especially with solids) since long term plants if left in with no solids filtration will get glommed up with gunk and start to suffer.  And if you were depending on your plant roots to provide bio-filter surface area then you have to be very careful to stagger your harvest and planting to keep your bio-filter stable.


I think u misunderstood. My understanding is that its often recommended to stock one pound of grown out fish per 5-10gal of water. However, its more common to see a pound to 5-7 gal of water. The second part I think u missed is the media beds will serve as bio-filtration and possibly get red worms. After bio-filtration in a media bed with heavy feeders such as tomatoes and peppers and then gravity feed to a raft bed with light feeders getting lowered nutrient level and filtered water from the media bed. The question is can I stock higher with the heavy feeders concept to like a pound of grown out fish to 3-4 gal of water? And how would I calculate it to b precise? I'm guessing trial and error at this point.
TCLynx said:

Ryan,

    You need enough bio-filtration for the fish load.  I'm not sure where you got 5 gal-10 lb of fish?  5 gallons of what? Your numbers actually sound a bit backwards to me.  I often do like 1-3 (depending on kind of fish) fish per 8-10 gallons of fish tank and I will have like 20 gallons of grow  bed to filter for it.  Now I tend to recommend light stocking densities and one should only figure they need more fish or nutrients if both of the following conditions are met.  1-the plants are showing signs of nitrate deficiency AND 2-the nitrate readings are 0.

I've found I can get away with a much lighter fish load even with some fairly heavy feeding plants provided the temperatures and aeration are right for the fish to be eating well.  That said, no matter what you still need the bio-filtration surface area to convert the fish wastes to plant nutrients.  Even if you have heavy feeder plants, if you don't have enough bio-filter, the ammonia and nitrite are going to kill your fish while the plants struggle.

Ya can't expect the plant roots to do all the filtration (especially with solids) since long term plants if left in with no solids filtration will get glommed up with gunk and start to suffer.  And if you were depending on your plant roots to provide bio-filter surface area then you have to be very careful to stagger your harvest and planting to keep your bio-filter stable.



Ryan said:


I think u misunderstood. My understanding is that its often recommended to stock one pound of grown out fish per 5-10gal of water. However, its more common to see a pound to 5-7 gal of water. The second part I think u missed is the media beds will serve as bio-filtration and possibly get red worms. After bio-filtration in a media bed with heavy feeders such as tomatoes and peppers and then gravity feed to a raft bed with light feeders getting lowered nutrient level and filtered water from the media bed. The question is can I stock higher with the heavy feeders concept to like a pound of grown out fish to 3-4 gal of water? And how would I calculate it to b precise? I'm guessing trial and error at this point.

 

Ryan, you're misunderstanding the relationships with regard to stocking density...

 

Stocking density is in the end totally related to your filtration capacity... (and oxygen provision)

 

More fish will certainly result in more wastes... ammonia for nitrification, and thus nitrates... and solids for mineralisation....

 

And tomatoes are known high nitrogen feeders...

 

But unless you stock your fish density to your filtration capacity... and/or remove solids.... then it becomes a mute point....

 

Because your system will become unbalanced... and loaded with suspended solids...

 

Remember that, with complete and effective nitrification... nutrients are being constantly replenished within the system... and constantly supplied to the plants...

 

You really don't need a lot of fish to produce copious amounts of veges....

 

Here's a dual system ... each side is stocked with (at that time) 100 x 100gm fish.... and is producing copious amounts of tomatoes, and other veges...

 

http://aquaponicscommunity.com/photo/albums/bamarang-project

 

http://aquaponicscommunity.com/photo/albums/bamarang-updates

 

And here's my latest system... about a month ago... with over 600 plants... stocked with 20 x 800gm fish (20 x 2lb)...

 

 

 

Ryan,

     I was only commenting on what you posted.  So are you saying this isn't what you meant to write?

I umderstand the general rule of stock density roughly being 5 gal - 10 per lb of grown out fish but that generally applies to growing traditional aquaponic crops, which are primarily light feeders.

It looked like you were saying 5 gallons for 10 lb of grown out fish???????  That is what worried me.  Looked to me like you had it backwards.  I would have said something more like 1 lb of grown out fish per 5-10 gallons of fish tank.  I suppose it is just how you typed it out made it easy to misunderstand.

But anyway, you didn't say how much media bed you would have to do the filtering.  If you have enough filtration, Heavy feeders will remove more nitrates and may leave less nutrients to go around but it doesn't necessarily follow that the stuff in the rafts would get less nutrients, it is all in solution and mixed throughout the system.  It isn't really like an assembly line, it isn't like the tomatoes are getting the first pick of nutrients and leaving little for the lettuce, it just doesn't quite work that way.  When people have tested nutrient level at the beginning of a portion of a system and after that portion of a system the nitrate levels don't seem to change measurably.  Like water, the nutrients tend to find their level.

Now I will say that I've experienced plants in media beds seeming to have better access to nutrients under less favorable conditions than the plants in NFT or Raft.  Seems that even in high pH situations the nutrients are still easier for the plants to access in the media than just floating in the water.


Hey Rupert, I understand the relationships a little better than u think but I don't think I gave enough information. Grow beds (I.e. - bio-filtration ratio of 1:1. Meaning 1 cu ft of grow bed per pound of grown out fish. I was just more curious of the concept of having a higher nutrient concentration going to beds properly sized to filter waste and properly planted with all heavy feeders to complete the mortification process and have the water then run through a raft system that has very light feeders, like lettuce and basil. The raft setup just feeds another type of plant and adds surface area for mortification bacteria. No one has really answered my question as to how I should calculate it but its going to b just a matter of playing with the test kit and +/- fish and/or plants to get the levels right. But roughly, I'm a lb of fish per 5 gal of water and 1 cu ft of grow bed per fish. I like ur setup. How are u filtering in terms of solids for ur nft channels?
RupertofOZ said:



Ryan said:


I think u misunderstood. My understanding is that its often recommended to stock one pound of grown out fish per 5-10gal of water. However, its more common to see a pound to 5-7 gal of water. The second part I think u missed is the media beds will serve as bio-filtration and possibly get red worms. After bio-filtration in a media bed with heavy feeders such as tomatoes and peppers and then gravity feed to a raft bed with light feeders getting lowered nutrient level and filtered water from the media bed. The question is can I stock higher with the heavy feeders concept to like a pound of grown out fish to 3-4 gal of water? And how would I calculate it to b precise? I'm guessing trial and error at this point.

 

Ryan, you're misunderstanding the relationships with regard to stocking density...

 

Stocking density is in the end totally related to your filtration capacity... (and oxygen provision)

 

More fish will certainly result in more wastes... ammonia for nitrification, and thus nitrates... and solids for mineralisation....

 

And tomatoes are known high nitrogen feeders...

 

But unless you stock your fish density to your filtration capacity... and/or remove solids.... then it becomes a mute point....

 

Because your system will become unbalanced... and loaded with suspended solids...

 

Remember that, with complete and effective nitrification... nutrients are being constantly replenished within the system... and constantly supplied to the plants...

 

You really don't need a lot of fish to produce copious amounts of veges....

 

Here's a dual system ... each side is stocked with (at that time) 100 x 100gm fish.... and is producing copious amounts of tomatoes, and other veges...

 

http://aquaponicscommunity.com/photo/albums/bamarang-project

 

http://aquaponicscommunity.com/photo/albums/bamarang-updates

 

And here's my latest system... about a month ago... with over 600 plants... stocked with 20 x 800gm fish (20 x 2lb)...

 

 

 

Not mortification, lol. Nitrification. :)

thank u tc. That makes sense, its most likely just going to level off the nutrient level. Not really an assembly line but at least the heavy feeders have the first stab at the nutrients everytime the water leaves the fish tank. But yea, I told someone else that I didn't give enough info. I should have started by saying a lb of fish per 5 gal of water with a cu foot of grow bed per lb of fish in filtration. Thank u for your responses, I understand the concept of the nutrient concentration leveling off throughout the system perfectly. I wad thinking it will deplete before the raft system due to the heavy feeders in media beds but it will find a medium nutrient level rather than the assembly line theory. Thanks.
TCLynx said:

Ryan,

     I was only commenting on what you posted.  So are you saying this isn't what you meant to write?

I umderstand the general rule of stock density roughly being 5 gal - 10 per lb of grown out fish but that generally applies to growing traditional aquaponic crops, which are primarily light feeders.

It looked like you were saying 5 gallons for 10 lb of grown out fish???????  That is what worried me.  Looked to me like you had it backwards.  I would have said something more like 1 lb of grown out fish per 5-10 gallons of fish tank.  I suppose it is just how you typed it out made it easy to misunderstand.

But anyway, you didn't say how much media bed you would have to do the filtering.  If you have enough filtration, Heavy feeders will remove more nitrates and may leave less nutrients to go around but it doesn't necessarily follow that the stuff in the rafts would get less nutrients, it is all in solution and mixed throughout the system.  It isn't really like an assembly line, it isn't like the tomatoes are getting the first pick of nutrients and leaving little for the lettuce, it just doesn't quite work that way.  When people have tested nutrient level at the beginning of a portion of a system and after that portion of a system the nitrate levels don't seem to change measurably.  Like water, the nutrients tend to find their level.

Now I will say that I've experienced plants in media beds seeming to have better access to nutrients under less favorable conditions than the plants in NFT or Raft.  Seems that even in high pH situations the nutrients are still easier for the plants to access in the media than just floating in the water.

Yea Ryan, you will just have to kind of trial and error to figure out the right balance.  Keep in mind that the balance will vary significantly by season, temperature, fish type, fish feed (protein %) and stage of plant growth.  I think you may find that the media beds (once the system is mature) will make a nice bit of nutrient buffer to help level out a bit of the fluctuations but there will still be fluctuations

And yep, if you have the (max) level of filtration built in... then you certainly can adjust stock levels to number/type of plants....

Yea, like when the tomatoes are going great guns and the fish load is maxed out but nutrients are low, it's probably too hot to plant lettuce in the rafts anyway so just leave some rafts empty.  When it gets cold and the tomatoes get pulled out you might have the rafts full of lettuce and greens and only plant the media beds as needed to keep up with whatever your nutrient levels are.

I'm still re-learning my balance since I've changed out media which has greatly affected pH, the plants all went crazy then the nutrient level dropped and suddenly I had plants showing signs of nutrient deficiency.  Part of the trick is keeping track and timing things since there will always be a delay before you see the results of most things to do with the plants.  On a backyard scale it is generally not a big deal but as you start trying to keep a steady (and pretty) supply of things for a market garden it becomes more challenging to get the balance right.

Key is keeping the bacteria happy and water quality good so you have a stable base to work from.

In  my process, I stock and grow much like everyone else. The main difference is that I "drain" half my tank every two weeks to another aerated grow bed in a succession of six beds. Each bed grows a different trophic level of plants. In my first bed I grow a choice of beans, peppers, melons, spinach and strawberry. The next level/ bed I grow eggplant roses and rosemary. Grains pea sage and thyme in the third. Orchids, parsley and lettuce in the fourth, with sprouts in the fifth and finally near clean water that grows algae in the last step. This near pristine water flows into the first out of six tanks to collect and build nutrients.

I hope this helps.

Cheers

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