Filtration Advice/Recommendations

[AB54]

Hello to all:
I'm new to this site, left an intro explaining the situation, but I'll reiterate.
My girlfriend hopes to over Winter a 1/2 doz 3" Koi in a 39g bowfront Topfin aquarium. The filtration system is wholly inadequate, we're having to do major H2O changes every 3rd day. I made a gravel vacuum, it's incredible the amount on trash the rascals generate.
I seek advice on an filtration set-up. I've read enough about Koi to know their not suited to captive living, but my gf is set on keeping them. Thanks

 

[Aiken Drum]

I would look at a canister filter rated for double the capacity of the tank.

Consider though that if you are cycled and your filter is cycling out waste to nitrate, a bigger filter wont cycle out waste to less nitrate. You might still be looking at twice weekly water changes for such a large bioload in a relatively small volume of water. The only way really to reduce the frequency of water changes is to get a bigger tank or reduce the number of fish. As the fish grow your situation will only get worse.

Given your plan in your intro post is to move the fish to ponds next spring, have you considered a bare bottom tank? Will at least make removing poop etc an easier process.

 

[AB54]

Thank You.

 

[Aiken Drum]

Do you know what your water parameters are? The issue will be if your filter simply isnt big enough to remove all the ammonia and resultant nitrite into nitrate. If you arent seeing any ammonia or nitrite there is no immediate need to get a bigger filter, but as the fish grow that could change. Even a double capacity filter might not cut it when the fish get bigger and go over the capacity of the tank.

 

[AB54]

Thanks again for the input. Best thing all around in my opinion is to put them in the pond and let Mother Nature take it's course. It's as good a pond as some I've seen. Otherwise mucho money is gonna be spent trying to keep fish not adapted to tank life, in too small an environment.
I'll let her read these posts...let her decide.