I recently purchased a couple of flowerhorns for 55 gallon tank. Water parameters were all good. The first fish was about 3 inches and died within two days. The second fish was a juvy and about 1.5 inches. This fish died in a day. Temperature was 78 and the tank earlier had an angel fish and some tetras (since moved to another tank). I thought flowerhorns were very hearty. I have two Eheim canister filters on the tank and keep the fish tank bottom clean of gravel. I added a little stress coat before adding the fish. What could I be doing wrong?