So I have a breeding harem (1M:3F) of multis in a 10 gallon, with a whole bunch of fry. Recently, the male has been acting strange - his mouth was always wide open, breathing rather fast. It almost looked stuck open. Today I woke up to him dead. I have not checked water params, but the presence of new and healthy fry suggests to me that things are fine. I perform 25% weekly WC. All other fish are acting normal and eating fine. I've had these fish for 4 months now - the only thing new was adding a nerite snail from my other tank to take care of some recent algae growth. Any idea what could have caused this?