cardinal sucking air...

[mandarine65]

.... from the top of the tank. I checked the sg and it's at 1.021 and all other parameters are right on. I just got him on Sunday and he seemed to have acclimated well. My fish book tells me this behavior can be from poisoning or the salinity could be off. Any ideas and how can I help him?

 

[swfishy]

You can also check your dissolved oxygen level. I have seen these fish do this in a lower dissolved oxygen situation.

 

[m0nk]

Is your SG always at that level? Are you checking with a hydrometer or refractometer? I'd use the latter whenever possible, a swing-arm hydrometer can end up getting stuck because of salt residue or something.
Also, what are your other parameters? You say they're good, but what exactly are they?

 

[rcreations]

Why do you keep your SG so low? You're right at the lowest acceptable level so any error with your reading can be bad for the fish. At least keep it at 1.023. That way if you're off a little, it's still ok for your fish.

 

[calaxa]

SG is fine if it is FOWLR. Large LFS keep theirs at 1.017-1.019 on their fish only systems to save salt. Personally, I would raise it to 1.023-1.025 as suggested to keep some snails and hermits.

 

[cranberry]

That sounds like an oxygen problem. Next you may see them listless and gasping on the bottom as they no longer can sustain themselves in the water column.