Please help! Our zebra danio acts like he's really sick and feels really bad. For about 3 days now he just drifts or floats at the surface, and then if we stimulate him (approach the tank, tap the glass, disturb tha water) he takes off and swims like crazy for a bit, then normally, then floats again. This morning he had made a little depression in the gravel between plastic plant and tank wall, where he just hangs out motionless until we tap the glass really hard, then he swims a bit and goes back. Sometimes when he swims he kinda drifts sideways or swims with his head way up and tail down.
No rashes or wounds, does not look bloated...he's a crimson Glofish, color now a little faded as if stressed.
He lives in a 2.5 gallon Aqueon tank established 5-6 weeks ago, cycled three days with no fish. Tank has a filter that came with it, a heater, and one other zebra danio, who seems totally healthy (we had three, lost the first one suddenly about ten days ago -- he did the "ok at bedtime, floating dead the next morning" deal). We've had real trouble controlling ammonia, due at least in part to food debris. This week with really aggressive gravel hygiene (vacuum), big water changes (about 80% 2 days ago), now we have ammonia 1 ppm, nitrate and nitrite at recommended levels near zero, pH about 6.2 to 6.6 (hard to keep it high enough). Temp. 72-78 F. We've added Stress Coat, Stress Zyme, and Prime.
If anyone knows what may be wrong and how to help, thank you very much!! They're such friendly, happy little fish and this little guy really is struggling bravely. I would hate to lose him, and also don't like seeing any creature suffer...