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I have about an 800 gallon system I builit with 18 grow trays. I have about 150 1- 2" gold fish. I was wondering wather the ratio should be per gallons of water in the system.

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That sounds good, but you may need to cull the fish if they get really big, or build a tank addition later on. How big are your grow-trays. Also, how deep are they and what medium if it has one at all. If there is no medium please tell us the type of filtration you have. Good luck!

Trays are 11' wide, 31" long and 6-7" deep. I'm using pea gravel. No filteration, other than the water every 45 minutes gets pumped to the top of the beds, and then when full they drain. So the wtaer is pretty clear. I addded some seaweed extract to get things started

Mike, the pea gravel is your filtration. I assume you mean 18 grow trays that are 11inches x 31inches by ~6inches deep correct? 18 of them at 11 feet long would be a lot.

So you should have 42sqft of grow space and @ 6inches deep, 160 gallons of pea gravel. 

160gallons of gravel filtration is how you want to gauge how much fish you can handle. The real question is, is 1 gallon of gravel per goldfish enough? That will depend on how big they plan on getting.

That seems like plenty filtration. Just watch your nitrates and ammonium levels.

Just read i should be addin g Calcium Hydroxide & Poatasium Hydroxide as additional items that the fish water don't provide. What do you think?

Mike, both those compounds are pH buffering compounds... you may have to use them as such, depending on your pH...

And certainly some Potassium and/or Calcium boost is beneficial for plant stages of growth... and required if you have deficiencies...

But if your pH is high... then you wouldn't use either of the two compounds to address a deficiency issue...

So you don't add anything to the water, just keep an eye on the nitrites and amoniona levels?

In dooing some reseach, I read that A good rule of thumb is to stock about 1 lb of fish per 5 -10 gallons of water, or 1-2 fish per 10 gallons of water. Never stock more than 1 pound of fish for every three gallons of water. Should we go by this, or the pounds of gravel and plant material?

That is a good rule of thumb assuming you are at the least a 1:1 growbed to fishtank volume ratio. That is indirectly 1lb (or 1-2fish) to 5-10 gallons of growbed (or filtration volume). The volume of water is important, but not as important as your growbeds capacity to filter the water.

FYI 7.5 gallons in a cubic foot, so 1 cubic foot of growbed to 1 fish (with a grow out weight of 1lb) is an ok rule of thumb I have seen TCLynx mention before. I like that rule the best.

Chris makes a very, very good point Mike. You should ALWAYS stock according to your bio-filtration capacity, and NOT your fish tanks water volume capacity.

Well, at some point you may need to add something. I suggest keeping to a pH of 7 (or, neutral) which may require you to either add an acid (Acetic Acid, or vinegar; HCl; HF; and so on) or a base (NaOH, this is very strong; Calcium BiCarbonate; Calcium Carbonate, sea shells/egg shells; etc.). Buy some pH testing solution from a hydroponics or aquarium store and follow the directions. Remember not to move the pH more than .1 per day
Mike Roe said:

So you don't add anything to the water, just keep an eye on the nitrites and amoniona levels?

We have a system near Albuquerque and we have had all sorts of problems with PH issues. What finally tipped us off that it wasn't the rocks but the water was a wonderful gentleman on this site who told me about how much acid he was adding daily due to the water in the Phoenix area to main PH.  I should have known that - I grew up there!  

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