Aggressive fish!

[Dadwallan]

Hi, first time poster and new to keeping fish!

I've owned a fluval 200 tank for a few months and the first fish were a pair of black mollies, since then one of the mollies died, I lost a couple of fish due to ammonia levels, I regularly change and test the water so the water condition is perfect.

The reason for the post is the behaviour of my remaining Molly. I have lost 4 guppys in the last month only one carcas was found which had been badly pecked, also I've lost 2 tetras, no carcasses again!

Last night the black Molly was found aggressively attacking a marble Molly which died later and today the same was occurring to a gold gourami , I have isolated the Molly but need some advice on
A solution.

Thanks in advance

 

[LyndaB]

Is your tank cycled now? What are your exact readings for ammonia, nitrite and nitrate?

If you had ammonia, your fish would've been highly stressed and, an otherwise peaceful fish, could have become irritable enough to attack its tankmates. Fish will also consume dead or dying fish to keep the tank bacteria level as low as possible. You wouldn't necessarily find bodies.