I have four Boeseman Rainbows and they are not looking well. And unfortunately, they are mimicking the same behavior I saw from my fifth that recently passed.

They are losing their color and tend to spend a lot of time swimming in place near the top of the tank or swimming in counter-clockwise tight circles.

They are also constantly opening and closing their mouths.

I have a 75g planted tank and the other inhabitants are 2 yoyo loaches, 5 adult platies and probably about 20 juvenile platies which I am moving out this week.

The water quality tests fine, with 0 ammonia, nitrates and nitrites.

The ph is 6.7, regulated by a CO2 system for the plants.

The temp is ~78 degrees F.

Any ideas on what may be wrong?

Thanks!

I would make a 1/3 water change and stop your CO2 system (your ph may be crashing) and see if your Rainbows imrpove. Rainbows usually like a ph above 7.0. You say you have Zero Nitrates, this isn't possible with a biologically active tank. You always have proteins decomposing to Nitrates. I have several Rainbows and I pay little atteention to the ph. They don't like dirty water though and will die on me if the water isn't clean.

Thanks. I redid the nitrate test and got 10ppm. I also turned up the bubbler to add more oxygen to the tank. Fingers crossed. The co2 system is connected to a Ph sensor, so it can't get to low.