MAX amount of large fish I can keep in an over filtered 1,500 gallon indoor pond


MFK Member
Sep 14, 2017
Crested Butte, Colorado

As some of ya'll may know, I have been working on a project recently that involves converting the extra fire suppression vats we have in our basement. The person that sold us our house put 3 in instead of the usual 1. So now I have 2 1500 gal tanks just sitting in my heated basement, ripe for the taking. I am going to convert 1, see how it goes, and possibly convert the other. I am planning on getting some serious filtration for these guys, so my question is how many fish can I put in each one? A better question is how many 20" or bigger fish can I put in each one? Also, is filtration rated for a few thousand gallons higher than the tank volume good? I am planning on keeping a lot in there, so I am going to go big on filtration. Answers to these questions would definitely be appreciated!

Here's some fish I'm planning on keeping at the moment. Keep in mind these fish will go in a MUCH larger outdoor pond in the coming years. I'm talking 1+ acres. Also, living in Colorado limits me to cold water fish for the most part.
Japanese Koi (getting the real deal imported from Japan!! So stoked!)
Golden Mahseer (goes into big pond later)
Siberian and Diamond sturgeon (same as above)
BIG rainbow trout. I've caught some over 15lbs. So should be fine with the bigger fish!
(MAYBE, not sure if I should get them or not) Chinese wels (found a iffy source where I can get them for about $10 a piece.)
American paddlefish
Chinese Phoenix barb
Albino channel catfish

I will probably evenly divide the species of fish into the two tanks. So it may look like a lot, but all of them will go into different tanks based on temperament.
ALSO: I have done my research on the paddlefish! So don't get scared.



Redtail Catfish
MFK Member
Dec 30, 2015
I think you are going about this in completely the wrong way imo.

You might have the most fantastic state of the art filtration on the planet that means you can keep your toxic levels of waste down to virtually 0ppm. That's great.

But what about the needs of the fish? Room to swim freely? Aggression levels? Basically keeping them in a stress free environment.

They may very well have nice water, but that's about it with what you are planning.

I wouldn't over cramp them too much, let them grow out stress free and then put your happy fish in your large pond at a later date.
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Jack Dempsey
MFK Member
Nov 24, 2009
Salish Sea
You should consider floor space, not just volume. Apart from that, though, you may want to check your state regulations to see if you need a license for some of those species. At a glance, it looks like you'd need a license for the paddlefish, the sturgeon, and the siluris species (Chinese wels). The cyprinids and trout look to be ok.
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