I set up my 55 gallon tank and let set for 3 days before adding fish. I added 2 corys and 3 zebra danios. and was getting ready for to add a few cichlids the next day and when i awoke i had dead and dieing fish. i did a test of PH and it was fine ammonia was detected but was just above normal. but the nitrites was way off the graph. what could have caused it?. i have gotten the nitrites back down but am worried about the nitrites going wacko again. and to add another question. will i be able to keep3 rams and 3 apisto. the tank has driftwood and is half rock and half planted. should i add more rock for this combo?