i have had many lumpheads die in the last month or so and usually in groups of 2 of 3 ,i have checked the ph, ammonia,nitrites etc and are all normal, the temps at 27 degrees so i dont see what is causeing it,they are in a 90litre tank with juvi afra (dogtooth) and no deaths from the other species only lumpheads .I recently brought new food (2weeks ago) because they didnt like my other food and are still dieing. I have no clue what is causeing it ,fed shelled peas last night . any ideas? can a disease only affect one species?