I have a 20G heavily planted tank it is about a year old. I am having trouble keeping ottos in the tank every time I get some they die within a month or so. I try to keep three in the tank but rarely have more that one live one. All levels are fine and all other fish are fine. ph is a bit high 7.6. I occasionally put malifix in the tank could that be it? They don't die right after I put the malifix in so I don't think that is the problem. I feed algae pellets but I've never seen the otto eating them. Anyone have any ideas?