bubbles on the water

Question
i have a 40-50 gal tank. it was a yard sale item! i have a submersible filter and only gravel and fish in it for the moment. i have washed everything very thoroughly and rinsed very thoroughly also. i have used start right and nothing else in the tank. my fish (9 zebra denials) have been in there for about 2 weeks maybe a lil less. over the last 4 days bubbles have been forming on top getting more and more. i was about to do a cleaning by removing 1/4 of the water and replacing it. but i don't know what the bubble are about. 1 of them have a very full belly but all are very active and seem very happy fish. when time to feed they come right to the top and no heisting to eat. i remember Reading somewhere this is a sign of some sort of infection or something like ick or something.(they have no white spots or anything so i know its not ick they don't rub themselves either) can you help me with this? that would be great thanks. Jason

Answer
Hi Jason,

Do you happen to have a water test kit, or can you take a sample of water to your pet shop and have it tested?  My first thought is bad water quality.  I would not hesitate to do about a 30% water change at this point to see if you can clear it up at all, AND get your water tested to see what your parameters are.  Danios are hardy fish that can survive in a lot of different types of situations, so they sometimes are not a good indication of what is going on.

You say that one has a "very full belly".  Do you mean as in "chubby" or does the fish's scales and body look swollen up, somewhat resembling a pinecone?  That would also help if you could tell me more about how he/she looks.

It's really hard to say at this point what may or may not be going on.  That's why I would definately start with the water change and go from there.  Make sure you "skim" the bubbles off the top while you're changing the water.  Also, be sure to use water conditioner and replace the water with water that is about the same temperature as what you took out.  I would also add 1 tablespoon of aquarium salt per 10 gallons.  Salt will help the danios in case they are undergoing any type of stress at this point, since it is a new tank.  Remember, salt does not leave the tank, except with water changes.  So be sure to replace the salt taken out when putting water back in (i.e. if you take out 5 gallons of water, you put 1/2 tablespoon of salt back in).  Try to dissolve it as much as possible before putting it in.

After you have done all this, get back to me and let me know your water parameters and how things are going, and then we'll go from there.

I will wait to hear from you.  Good luck!!  ;o)