ok well, was 4 now trhee occupants, one got isolated cause she was really sick,... and still kinda is..., but she isnt floting as much now, yaya, anyway off topic, um, 4 foot by 1 foot by 1 and a bit foot, water cahnges at least once a week with about 50% gone, ok i'll get onto the thing with the pet shops, will do, but how do i know what is good and what is bad? athnk you for this by the way, the water is 20-22 dgrees celcius