my angel fish

We recently bought 3 angel fish for our new tank. We were told that the dark blue fish was a male, and had to be sold with his mate. We know you have to be careful what you put in the take because the fight. The other fish was 2 Sucker fish, and another female Angel fish. Well long story short we lost the husband and wife as well as one of the sucker fish. We set the tank up about 2 weeks before and tested regulary the levels of ph,nitrate etc. The one female is still holding on, as well as the other sucker fish. The female Angel fish seems very lathagic, and lays under the water filter, almost motionless, a couple of times I thought she was dead. The Sucker fish does not cling to the glass but hangs out on the bottom of the tank. He doesn't seem to lively either. Please help. I have checked the levels within the tank and all seems well. We do have three live plants. Thank you in advance.
-Crystal

Angels are susceptible for diseases and it is important to quarantine them for few weeks before placing them in the display tank. In fact you are supposed to quarantine any thing you buy for the tank to see if it is carrying any viruses or bacteria.

What you can do at this stage is quarantine the fish and administer medicines for a while, but you'll have to go to a pet shop for this purpose preferably with the tank or at least the fish if the tank is too big.

If the aquarium was set up for only two weeks, it had probably not finished cycling. Tanks that are not fully cycled or properly maintained will have excess ammonia, which is toxic to fish, especially angelfish. In addition, those sucker fish become active at night; one of their favorite foods is the slime coat of other fish.