Determining Stocking Capacity For Large Fish

[JBlacksmith]

I have a question aimed toward the more experienced aquarists: I know that the one inch per one gallon guideline is just that, a guideline, and it is really only useful for fish of roughly two inches or smaller. How does one go about estimating stocking capacity when the fish are larger than three inches?
 
I have read somewhere that monitoring nitrates will tell me when my tank is full. I read somewhere else that I should be measuring the oxygen and CO2 levels in my tank. In another source, a mathematical formula was created for the dimensions of my tank in comparison to the dimensions of my fish (taking into account their activity level about the tank). Other than that, my research has not turned up much information that is commonly agreed upon. Thus far, I have resorted to understocking (at least I hope it is understocked) my larger aquarium until I am certain it can house more fish. Can anyone on here help?

 

[fluttermoth]

This is why stocking is more of an art than a science!
 
I'm afraid there are no easy 'rules' you can use.
 
For bigger fish, dimensions of tank is the first priority. Sedentary fish should have at least 5 times their adult body size in length of tank (8 for more active fish) and at least twice in width. So a foot long oscar needs a five foot tank; a foot long bala shark needs an 8'.
 
Then you have bioload. You want to aim to have your nitrates getting to no more than 20ppm higher than your tap water; that might mean less stock, or more frequent or larger water changes.

 

[JBlacksmith]

This is why stocking is more of an art than a science!
 
I'm afraid there are no easy 'rules' you can use.
 
For bigger fish, dimensions of tank is the first priority. Sedentary fish should have at least 5 times their adult body size in length of tank (8 for more active fish) and at least twice in width. So a foot long oscar needs a five foot tank; a foot long bala shark needs an 8'.
 
Then you have bioload. You want to aim to have your nitrates getting to no more than 20ppm higher than your tap water; that might mean less stock, or more frequent or larger water changes.

Thanks, that makes sense! Now, the easiest way for me to imagine this is a tank of certain dimensions housing one large fish of certain dimensions. In reality, I prefer to keep community aquariums. How do I go about filling in the little fish after I have fulfilled the large fish's needs? Would I need a tank larger than the large fish requires before I could add smaller fish?

 

[fluttermoth]

For that you need to measure nitrate; in your tap water and in the tank before and after a water change.
 
'Overstocking' is really only an issue if your maintenance regimen is inadequate. Think about Rift Valley/Malawi set ups, that are routinely overstocked to keep aggression in check. Those set ups are perfectly viable, but their keepers need to be aware of the need for heavy filtration and large regular water changes.

 

[JBlacksmith]

Thanks so much for your help!