I have seven adult angels, five in one tank and two in another. They are very easy to breed once they are mature. If you get six or more juvenile angels, the chances of getting a breeding pair is in greater than 90%. They are also gorgeous fish. Not a whole lot of fish can go with an angel...
I had two fully grown angels that were a breeding pair. They had a pink kissing gourami as a tankmate. They picked on this poor guy relentlessly. I added three juvenile angles and the gourami thought they were his new best friends. The adult pair also stopped picking on the gourami and have...
Your biggest concern would be the health of the new fish. They might have something that your old fish might not be able to handle. Add one of your old fish in with the new fish and wait a couple of weeks. If all is well with the health of your old fish, it will probably be ok to add the...
It might be some gravel dust that managed to allude you. Or it could just be a bacteria bloom caused by the addition of your two new fish. Since adding new fish disrupts the cycle of the tank. Or you might have added them before the tank was cycled and the bio load is too much for the filter.