Bizarre behavior

[gznllf]

I have 8 cardinal tetras that I bought 6 weeks ago. They are very healthy fish until I feed them. When I add flake food (which stays on the water surface). They come up to the top and eat. Then almost immediately some of them and sometimes all of them start swimming down then start rising to the top. They are basically swimming down and fighting to keep from floating to the top. They are in the vertial position and there tails are floating to the surface. They can't eat when they're in that position. They obviously are taking in air bubbles as they get the food as the air bubbles sometimes come out of their mouths. After 15 minutes or so they are back to normal. I didn't think it was that big of a deal until this morning when one floated to the top and was on its side. I'm sure if I wouldn't have flicked it with my finger it would have died. I have a whisper filter which I have on a low setting. All I can think of is that it's a surface agitation problem which I have never heard of.

30 Gallon tank
Chlorine, Nitrites & Nitrate - normal
Whisper filter (bigger than I need for my tank) - keep on low setting
PH - 6.5
Temp - 75
Community - The cardinal that I bought & one small clown loach

 

[Alien Anna]

I've never had much luck with cardinals. If I can get them to survive the first couple of months, they're generally OK, but it's getting them to that point that is the difficulty.

You say chlorine and nitrite are "normal" - I presume you mean you've detected no chlorine or nitrite in the water? Have you checked for ammonia?

If that's fine, what are your nitrate levels? Since they come from the wild, with naturally very low levels of nitrate, Cardinals can be intolerant to levels that native born fish don't even notice.

I'd suspect some kind of infection in your fish, perhaps the early stages of Swim bladder disease. I'd do very regular water changes and put some Melafix in your tank. Keep some Interpet Internal Bacteria, and Swim Bladder Disease remedies on stand-by, in case any fish starts to show obvious signs of disease. Put an air-stone in too, at the opposite end to the filter - it may be that the filter's on so low it's not oxygenating your water very well.

Another alternative is that your gravel has "dead spots", that is spots of anaerobic bacteria that produce sulphur dioxide gas (a poison). Dead spots can occur under bogwood or rocks, particularly if you have deep gravel and haven't been sufficiently diligent in cleaning it (without over-cleaning it and killing off the beneficial bacteria). However, my experience is that this generally causes a nasty whiff in your tank and kills fish, rather than making them a bit unwell.

 

[gznllf]

Thanks for your help. My nitrite, nitrate & ammonia levels are fine. The fish only react this way when they come up to get food on the surface. 5 or 10 minutes later they are fine. Other than this they are perfectly healthy. I'll try putting in an airstone.