behaviour change

Question
I had an angel fish that died recently. It died because it was swimming upside down. I also own other angel fish. when the angel fish died, the others changed in behavior, they weren't hungry anymore, usually they were ALWAYS hungry and active, moving around. But now they are always at the bottom and hiding behind plants. what happened and what should i do?
I own a 10 gallon tank, undergravel filter, 7.0 pH, I'm not sure what ammonia or nitrates are. i feed them fish flakes and sometimes freeze dried bloodworms. there is a lot of water movement in my tank.

Answer
Hi Karen,
Ammonia, and nitrites if present in your water will kill all of your fish.  You must have your water checked at the pet store, or buy these test kits.  They are always handy to have, and should be number one in your fish cabinet.  I would also like to mention that Angel fish need lots of space.  One angel fish needs 10 gallons of water, two angel fish, 20 gallons, and so on.
If you have ammonia or nitrites in your water, this would be the problem.  Make sure that your ammonia level is zero, and nitrites zero.  This is important for all fish.  Your water chemistry must be perfect.  Also, check that your fish have enough oxygen.  There must be lots of water movement in the water.
Have your water tested, then write back to me.
Lynda