Worried about my new fishies

[Ededdandeddy]

Hi,I've had two mollies and two neons in a tank for about a month now with no problems so far, but overnight one of the mollies has suddenly become a recluse and won't come out of hiding, even when I put food in I don't have any means to check nitrate or pH levels as of yet, the assistant at the pet store said I wouldn't need to do that until I had populated the tank a bit more. I can see him among the plants, he's just been swimming vertically for head down all day. Up until this morning he was the most energetic of the four fish in the tank I don't understand what's happened him


Any thoughts?
A

 

[molliwopp]

Could have air in his swim bladder. Did the guy at the lfs mention anything about cycling a tank? If youve only had the tank a month it wont be cycled and youll have alot of ammonia in the tank. Do a large water change of 50% as soon as you can and you might save your molly.

You really need an ammonia nitrite test. Without it you should be doing large changes until your tanks cycled.