ok so today was water change day .. changed water on 5 tanks .. but having problems with the 150 ... the rays are doing fine and 2 larger dats are doing well .. but my 2 smaller dats are not doing well at all .. both are breathing really fast and one was laying on its side on the bottom of the tank .. im kida stumped on why just the 2 small dats would have such a hard time... any ideas? ... didnt treat the water with anything .. never do ... and always do water changes the same .. water test fine nothing out of normal ..