Question
Hi there, i need some help! I've had my goldfish for 10 years and they have been fine until now. i have recently moved house and since the move i have notice my fish are acting really strange. They are swimming to the bottom of the tank and bashing themselves off the gravel? do you think it may be the water? i bought a few other fish a few month ago but 2 of them have died. could they be diseased and passing it on to my other fish? i also got an air pump but surely that wouldn't do any harm?
please help!
Chris

Answer
That sounds exactly like what has happened.  Typically, it is recommended to "quarantine" any new fish for a period of 1-2 weeks for observation and potential treatment.  You should be able to find a couple of decent articles online.  Look for any raised scales, as this would be a sign of parasites and can easily be dealt with.  Bacterial infections, which usually produce ulcers, are slightly harder to deal with.  They are still treatable and should not be cause for great concern.