Advice onindoor tank odor

[MIKE M]

I need advice on controling odor in my indoor tank.  I have a 500 gal tank with two 55 gal  mechanical filters. I also do a 20% water change every week. There are 12 koi ranging from 8 to 4ins. I also have a very good supply of air to this tank. 

[Sean]

It sounds like a bacteria bloom (a good thing). If this is a new tank set up, you can be pretty sure that is what this is. Your water is probably a bit cloudy as well which  is a sign of a bloom in progress.

Another note, your filtration may not be sufficient for the fish load, try feeding the fish less.

Do you have gravel in the bottom of the tank? if so, you may need to suction the gravel to remove excess fish waste. An under gravel filter will increase the biological filtration of the tank as well as assist in eating up much of the waste.

Cheers,
Sean

[MIKE M]

I am thinking that I may be feeding to much. I will cut back some what and see if this helps.

[Julles]

I have a lot of bettas, all in seperate jars.

One of those jars always seems to have a funky, rotten-ish odor, even a day after the weekly water change.

I figured it was one of two things:

-that was the only betta tank with a snail in it, so possibly the snail had to do with it
-some malady of that particular fish

I have a feeling it is #2, as that fish never seemed particularly vibrant or lively, as compared to the other fish.

So... perhaps there is something inherintly wrong with one of the FISH, instead of your husbandry?

Just a theory.

I would also suggest thoroughly cleaning the gravel, or even removing it.  And also use one of those scrubby sponge things to clean the glass and other surfaces in the tank (filter, decorations, etc.), in case the odor is connected to something adhering to those materials.