Fish at top of tank

Question
QUESTION: I have a 40 gallon tank with 5 goldfish and 4 quarry cats in it...and 2 snails. yesterday the two big goldies started gasping for air at the top of the tank. i did some research online and it suggested that there might be too much ammonia in the water. i did a complete change of water and now today they are still doing the same thing. i have an air stone in the tank as well so i don't know why they are doing this. any ideas?

ANSWER: Hi Nick,
 In general it is not a good idea to do a complete water change. That totally disrupts the system of an aquarium.  You are much better to do more frequent partial water changes.  In fact, you should normally be changing 25% of the water in the tank, once a week, every week.  

 Do you have a proper filter in the tank?

 Another possibility, particularly if the two goldfish were up in a corner is that one of the other fish is chasing/bothering them. Is that a possibility?

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>


---------- FOLLOW-UP ----------

QUESTION: i initially did a 25% water chance but a day later they were gasping again. after seeing this i replaced about 75% of the water and added a water treatment to replace the bacteria and what not. i have a 60 gallon filter so i dont see this being a problem. the two fish that go to the top are the two biggest ones so i dont think they are being chased. i have also noticed that when i get home from work or get up in the morning and the lights are off in the tank that are at the bottom but when i turn the light on that they gravitate towards the top. maybe they are drawn to the light...i dunno. thanks for your help.

Answer
Hi Nick,
 Size really doesn't matter in terms of them being attacked.

 Are they at the corner where you normally feed them?  If so, that is a very normal thing for goldfish to do, i.e., to "beg" for food.  They learn very quickly who feeds them and where they normally get fed.

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>