black mollies

Question
I've had 4 black mollies (alone) in a 10 gallon tank for about 2 weeks. I did a 10% water change at the end of the first week and since then they keep their fins down,even their tail closes, and they lie on the bottom of the tank. They aren't dead! They come up from the bottom when it's feeding time, other than that they just lie there. Very weird. Any ideas on what's happening? I used to have a 29 gallon tank and never had any problems like this. Is this tank too small?

Answer
Hi Kathy,
Usually in a bigger tank like the 29g tank, there is more room and time for error which can easily be fixed if caught early.  Since you downgraded to a 10g tank, there is 3x less room for time and error so anything adverse that happens in a tank will occur quick and must be caught before severe damage can done.  It is difficult to tell what is wrong with the fish, but Mollies are not usually inactive.  Lieing on the bottom of the tank is abnormal.

However, you stated that you have had the mollies for 2 weeks.  Is this is new tank and has just been set up 2 weeks ago? Or is it just the mollies that are new?  If it is a new setup, then the tank is not cycled yet.  And high ammonia intoxication can lead to heavy breathing and dwindling of activity.

During the cycling process of the tank you need to do a 15%-20% water change every 2 or 3 days depending how much you feed the fish to prevent nitrogen intoxication.  What you are trying to do during cycling is growing 2 sets of bacteria.  One that breaks down ammonia-to-nitrite and and another that breaks down nitrite-to-nitrate.  This process takes time and cant be rushed.  Cycling with fish can take anywhere from 3weeks to a month or maybe longer.  To measure the ammonia and nitrite toxicity in a tank, you must buy a liquid test kit available at most pet stores.

Let me know if you have any further questions
-Matt-