Whether or not the angelfish problem is related to the water quality, which it probably is, you DO have an issue with your water. The tank is cycling, and ANY ammonia and nitrite is extremely stressful to fish. I'm not sure what you mean by "working out the nitrite". Ammonia and nitrite are always zero in a cycled tank, and at this point your best option is a water change. Continue to do frequent water changes until the tank cycles.