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Hi all, 

First post here and looking for some advice on a new system design.  I want to build a combination of deep water raft and media beds with worms.  The current idea is  this:

500 gallon fish tank with 150 lbs of fish (Tilapia or Koi)

48 sq ft of media bed, 12" high with 2.5 lbs worms

500 sq ft of 12" deep raft troughs.

The question is will the media bed and worms be enough to filter the solids from the fish tank or should I put in a swirl filter, degassing tank and biofilter after the media bed and before the dwr?

Thanks in advance for comments and suggestions.

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150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

The 150 lbs of fish is for both the media/worm beds and the DWC.

Jonathan Kadish NYC AA Chair said:

150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

It's going to depend a lot on the direction of flow in your system. If water with that amount of solids is pumped directly into your deep water beds you will have problems with solids clinging to the plant roots and starving them of oxygen and also settling in the DWB's. You may also have problems with that many Koi in the 500 gal tank.

Ross,

I agree that if it goes right into the DWC then it is a problem.  My question is should I put it between the media/worm beds and the DWC or before the media/worm beds?

Ross Williams said:

It's going to depend a lot on the direction of flow in your system. If water with that amount of solids is pumped directly into your deep water beds you will have problems with solids clinging to the plant roots and starving them of oxygen and also settling in the DWB's. You may also have problems with that many Koi in the 500 gal tank.

I understand that the waste is for the whole system but the waste is only filtered by the grow bed. The concern would be distributing your waste and if there is too much solid waste you will develop anaerobic zones in the grow bed

Clinton Kripki said:

The 150 lbs of fish is for both the media/worm beds and the DWC.

Jonathan Kadish NYC AA Chair said:

150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

I think but would like some confirmation that the worms will be able to handle that much waste and the media/worm beds would not develop anaerobic zones.  The amount of fish is on the low side when you look at the total volume of water in the DWC.  It is my thinking that the DWC acts a sort of sump area for the media beds but it gives me plenty of sq ft to grow.  

Jonathan Kadish NYC AA Chair said:

I understand that the waste is for the whole system but the waste is only filtered by the grow bed. The concern would be distributing your waste and if there is too much solid waste you will develop anaerobic zones in the grow bed

Clinton Kripki said:

The 150 lbs of fish is for both the media/worm beds and the DWC.

Jonathan Kadish NYC AA Chair said:

150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

I learned these concepts from Dr. Rakocy & Dr. Lennard at an AP workshop. The way I think of it is system input vs output. Your fish food stays in the system until you take out either plant material, worms, fish or solids. Plants actually take very little out of the soil or grow bed to create vegetation or fruit. They use the nutrients as building blocks to assemble complex molecules through carbon fixation. Most of the weight of the plant is water and then molecules derived from carbon dioxide. So if you put a couple of pounds of food a day into your grow beds you might end up with a lot of worms & a lot of bacteria in your grow bed which may create toxic levels of nitrates for your fish and plants. My view in system design is that less fish is better for the overall health of the system. If you need more fish than you need more filtration.

Clinton Kripki said:

I think but would like some confirmation that the worms will be able to handle that much waste and the media/worm beds would not develop anaerobic zones.  The amount of fish is on the low side when you look at the total volume of water in the DWC.  It is my thinking that the DWC acts a sort of sump area for the media beds but it gives me plenty of sq ft to grow.  

Jonathan Kadish NYC AA Chair said:

I understand that the waste is for the whole system but the waste is only filtered by the grow bed. The concern would be distributing your waste and if there is too much solid waste you will develop anaerobic zones in the grow bed

Clinton Kripki said:

The 150 lbs of fish is for both the media/worm beds and the DWC.

Jonathan Kadish NYC AA Chair said:

150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

If I am only using the fish as a feed conversion to get ammonia and thus nitrates into the system (not to necessarily harvest them), how many lbs of fish are needed for this design?  You mentioned 20lbs before, how did you come about this number?  Is it a feed conversion rate?  

I was hoping that the worms would convert the fish solids/waste to usable nutrients and also eliminate the need for solids removal as the worm castings would be fine enough to flow through the DWC and have a dense planting of lettuce act as a biofilter in the DWC. 


Jonathan Kadish NYC AA Chair said:

I learned these concepts from Dr. Rakocy & Dr. Lennard at an AP workshop. The way I think of it is system input vs output. Your fish food stays in the system until you take out either plant material, worms, fish or solids. Plants actually take very little out of the soil or grow bed to create vegetation or fruit. They use the nutrients as building blocks to assemble complex molecules through carbon fixation. Most of the weight of the plant is water and then molecules derived from carbon dioxide. So if you put a couple of pounds of food a day into your grow beds you might end up with a lot of worms & a lot of bacteria in your grow bed which may create toxic levels of nitrates for your fish and plants. My view in system design is that less fish is better for the overall health of the system. If you need more fish than you need more filtration.

Clinton Kripki said:

I think but would like some confirmation that the worms will be able to handle that much waste and the media/worm beds would not develop anaerobic zones.  The amount of fish is on the low side when you look at the total volume of water in the DWC.  It is my thinking that the DWC acts a sort of sump area for the media beds but it gives me plenty of sq ft to grow.  

Jonathan Kadish NYC AA Chair said:

I understand that the waste is for the whole system but the waste is only filtered by the grow bed. The concern would be distributing your waste and if there is too much solid waste you will develop anaerobic zones in the grow bed

Clinton Kripki said:

The 150 lbs of fish is for both the media/worm beds and the DWC.

Jonathan Kadish NYC AA Chair said:

150 pounds of fish is quite a lot for 48 sq feet and no filtration. Feed rates should be reduced greatly with no filtration - I have heard from those who know that it is a nearly 85% reduction in the amount food input into the system. So if your objective is to have 150 pounds of fish then filtration will be needed. If you are ok with 20 pounds of fish then you may not need it. I grow with just 1 pound of fish per 4 sq ft of grow bed or about .4 grams per square foot of food per day - but then again I don't have the DWC addition or worms.

The feed rate for a typical UVI type DWC set up is 6g - 10g per square foot of grow space per day [numbers directly from Dr Rakocy] Also in the same conversation was mentioned that if you are not filtering the solids you would need around an 85% reduction in the feed rate because all of the nutrients stay in the system. In the UVI design more than 50% of the net weight of the food is removed as waste. So as you can see the amount of feed goes down to 1-2 grams per day per square foot if you are not doing any filtration.

You are doing a hybrid system so you will need to wing it a bit. Fortunately the amount of food you can feed a fish can vary because they don't require much to live. You will find a happy medium after some tinkering. I am just warning you from stocking too heavy to avoid a biological meltdown.

Thanks, good info, I will see what I can formulate from it and start with less fish and add if needed.

Jonathan Kadish NYC AA Chair said:

The feed rate for a typical UVI type DWC set up is 6g - 10g per square foot of grow space per day [numbers directly from Dr Rakocy] Also in the same conversation was mentioned that if you are not filtering the solids you would need around an 85% reduction in the feed rate because all of the nutrients stay in the system. In the UVI design more than 50% of the net weight of the food is removed as waste. So as you can see the amount of feed goes down to 1-2 grams per day per square foot if you are not doing any filtration.

You are doing a hybrid system so you will need to wing it a bit. Fortunately the amount of food you can feed a fish can vary because they don't require much to live. You will find a happy medium after some tinkering. I am just warning you from stocking too heavy to avoid a biological meltdown.

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