I have a 90 gallon tank left my aqua clear on for week while getting marineland ready gravle on bottom about 15 fish at first was having bubbles coming out of return which I read a lot of people complaining about re did the filter stoped some still see some coming out but not as much tested water said my ph off a little so maybe I will try and fix that do a water change see if that helps someone said put l of the aqua clear back on not going to be happy if I have to do this since I never had prob with them just that after 15 years I thought they were getting old and time to up grade guess what they say if not broken leave it alone lol