How to figure stocking in a mixed system

[TCLynx]

This is definitely a subject that doesn't have much study behind it yet.

 

At one point some one asked me how many fish they could keep in a 1000 gallon fish tank if they had a 4' by 8' 12 inch deep gravel bed plus a 4' by 32 foot raft bed?

My initial inclination would be to figure the amount of fish the gravel bed would support and then figure the amount of fish the raft would support based on the Friendlies Low density methods.  However, such a design is likely to overload the gravel bed with solids if all the water is going through the raft bed first.

 

I also tend to figure based on filtration and am not too worried about the nitrate levels and plant uptake of nutrients.  Seeing as the filtration must be up to the task or the entire system can crash and leave one with lots of dead fish to dispose of.  If the nitrates get too high one can simply add more plants/greedier plants, reduce feed for a bit, or water some soil plants and top up and if there are too little nutrients, one can simply pull out some plants for a while while.  This is easier with rafts/NFT as pulling and replacing plants doesn't stir up the system much.

 

My basic rule for stocking with the media based portion is 1 fish (grow out to 1 lb) per 7 gallons of grow bed (that would be the recommended stocking level.)

 

Then for the low density raft stocking (I don't know this one as well) but I think it is supposed to be around 3.5 square feet of raft space per pound of fish.  (This is because the low density raft system doesn't remove the solids and therefore the system has more nutrients in it per unit of feed given to a particular amount of fish.)

 

So for the above example,

4x8 gravel bed provides 32 cubic feet (7.5 gallons each) so the gravel bed could support 32 fish up to 1 lb each.

4x32 of raft is 128 square feet divide by 3.5 = 36.5 fish up to 1 lb so I add those together and get 68.5 fish supported by the filtration.

 

Again, this is just how I estimate an appropriate fish load for the filtration, keeping in mind that the gravel bed probably could become overwhelmed by the solids from such a fish load long term.

 

Also, the appropriate recommended numbers are from a "backyard" low maintenance point of view and stocking for commercial situations will be different and proper monitoring of dissolved oxygen to make sure the fish don't die overnight or during a power outage is important at higher commercial stocking levels.

 

[Harold Sukhbir]

In the Preamble it says;

"At one point some one asked me how many fish they could keep in a 1000 gallon fish tank if they had a 4' by 8' 12 inch deep gravel bed plus a 4' by 32 foot raft bed?

My initial inclination would be to figure the amount of fish the gravel bed would support and then figure the amount of fish the raft would support based on the Friendlies Low density methods.  However, such a design is likely to overload the gravel bed with solids if all the water is going through the raft bed first."

 

Since the raft demands(fish/lb) are even higher than the value for the beds means we have to deal with more than 50% of the waste. I'm thinking, the design of the digester will have to provide greater surface area than even the 4 x 8 bed and may be too big for practical purposes.

[TCLynx]

That is only the case if you are going by the UVI rates of feeding which assume solids removal.  If you are not removing the solids and you are mineralizing them in the system, you do not need so much fish or fish food to support the same amount of raft.

Harold Sukhbir said:

Since the raft demands(fish/lb) are even higher than the value for the beds means we have to deal with more than 50% of the waste. I'm thinking, the design of the digester will have to provide greater surface area than even the 4 x 8 bed and may be too big for practical purposes.

[Kobus Jooste]

Sorry to fall into this one a bit late, but I am going to experiment with a modified version of an aquarium trickle filter to see how it goes.  I have a 150 liter sump tank mounted 2/3 way up against the side of my fish tank.  It has dual inflows and currently, under passive flow, a lot of fines is settling out into it.  I am going to put a lot of net and bulky floating net balls into it, and then put a small pump at the far end of the filter tank.  The flow through should trap more fines, and as the unit is small and the organic load relatively light, the DO levels of the tank should regulate the filter tank and keep it OK for as long as solids build-up is not greater than what the set-up can mineralize.
 
Harold Sukhbir said:

TC said; "or do you have to suck the solids out of a setting tank and place them in the digester?"

If we want to remove 50% of solids for processing, we can simply divide the flow from the pump with equal size pipe, if we need more or less, we can manipulate flow rates.The digester could possibly be a large swirl/net combination filter with constant aeration. With this, solids can remain for longer periods in the system to mineralize and not run the risk of the system becoming anoxic because of the presence of large amounts of oxygen. Although some of the solids will have to be eventually removed periodically, overall we can increase the bio-availability of nutrient for our plants. In clarifier's and net or swirl filters nutrients are underutilized and valuable nutrient wasted.

 

[Harold Sukhbir]

Combination bio-filter/filter. I think going after the fines in this way will definitely speed up the mineralization process rather than allowing them to loop their way over and over through the system. Your hungry bacteria will take up residence in those net and net balls and devour them as they enter. Of course the more bio-filtration we add the more oxygen they deplete.

Kobus Jooste said:

Sorry to fall into this one a bit late, but I am going to experiment with a modified version of an aquarium trickle filter to see how it goes.  I have a 150 liter sump tank mounted 2/3 way up against the side of my fish tank.  It has dual inflows and currently, under passive flow, a lot of fines is settling out into it.  I am going to put a lot of net and bulky floating net balls into it, and then put a small pump at the far end of the filter tank.  The flow through should trap more fines, and as the unit is small and the organic load relatively light, the DO levels of the tank should regulate the filter tank and keep it OK for as long as solids build-up is not greater than what the set-up can mineralize.
 
Harold Sukhbir said:

TC said; "or do you have to suck the solids out of a setting tank and place them in the digester?"

If we want to remove 50% of solids for processing, we can simply divide the flow from the pump with equal size pipe, if we need more or less, we can manipulate flow rates.The digester could possibly be a large swirl/net combination filter with constant aeration. With this, solids can remain for longer periods in the system to mineralize and not run the risk of the system becoming anoxic because of the presence of large amounts of oxygen. Although some of the solids will have to be eventually removed periodically, overall we can increase the bio-availability of nutrient for our plants. In clarifier's and net or swirl filters nutrients are underutilized and valuable nutrient wasted.

 

[Kobus Jooste]

I think, and you are welcome to correct me if I am wrong, that even if the fines are just floating around in the system, they will be colonized by bacteria in any case - kind of as in a bio-floc / greenwater system.  Putting in the fines trap is just going to concentrate them in one place.  Trick would be to keep that area from going anoxic, but as I am planning a "draw through" type of set-up, the only issue will be dead spots developing over time.  A cleaning regime for the net balls should sort that out.

Harold Sukhbir said:

Combination bio-filter/filter. I think going after the fines in this way will definitely speed up the mineralization process rather than allowing them to loop their way over and over through the system. Your hungry bacteria will take up residence in those net and net balls and devour them as they enter. Of course the more bio-filtration we add the more oxygen they deplete.

Kobus Jooste said:

Sorry to fall into this one a bit late, but I am going to experiment with a modified version of an aquarium trickle filter to see how it goes.  I have a 150 liter sump tank mounted 2/3 way up against the side of my fish tank.  It has dual inflows and currently, under passive flow, a lot of fines is settling out into it.  I am going to put a lot of net and bulky floating net balls into it, and then put a small pump at the far end of the filter tank.  The flow through should trap more fines, and as the unit is small and the organic load relatively light, the DO levels of the tank should regulate the filter tank and keep it OK for as long as solids build-up is not greater than what the set-up can mineralize.
 
Harold Sukhbir said:

TC said; "or do you have to suck the solids out of a setting tank and place them in the digester?"

If we want to remove 50% of solids for processing, we can simply divide the flow from the pump with equal size pipe, if we need more or less, we can manipulate flow rates.The digester could possibly be a large swirl/net combination filter with constant aeration. With this, solids can remain for longer periods in the system to mineralize and not run the risk of the system becoming anoxic because of the presence of large amounts of oxygen. Although some of the solids will have to be eventually removed periodically, overall we can increase the bio-availability of nutrient for our plants. In clarifier's and net or swirl filters nutrients are underutilized and valuable nutrient wasted.

 

[Harold Sukhbir]

Interesting that you should mention bio-floc. It is a food source as well as nitrogen remover, how about designing our remote stations with this type of bacteria, well oxygenated, and intermittently "pulsed" in the loop? Can this technology be            in-cooperated into AP? I've read that bio-floc can promote fish growth from 10x -40x, and no telling what it can do for plants! Do you have any studies on this?

[Kobus Jooste]

My bio-fertilizer research started its life as an attempt to harness the ideas of bio-floc technology into an aquaculture venture with a modified filtration system.  Unfortunately, the relatively low maximum stocking densities of bio-floc systems forced me to "isolate" the bio-floc process in a seperate unit that is not connected to the main water supply.  Bio-floc also gets very soupy, with a TSS load that will force you to look at media beds only.  Then you automatically have media filtration that will interfere with the floc tank...............I think for me at this point in time, it is an interesting low density system, but one that I have noty tried to incorporate into typical AP.

Harold Sukhbir said:

Interesting that you should mention bio-floc. It is a food source as well as nitrogen remover, how about designing our remote stations with this type of bacteria, well oxygenated, and intermittently "pulsed" in the loop? Can this technology be            in-cooperated into AP? I've read that bio-floc can promote fish growth from 10x -40x, and no telling what it can do for plants! Do you have any studies on this?