Originally Posted by
Rev
lion has it nailed.I went through this a month ago when I swapped out some bio balls.It was explained to me as a bacterial bloom.All is fine now,took about 3 weeks to get back to crystal clear.
There is nothing wrong with Bio-Balls. If there is a filter media pad above them to filter the water before it hits the balls, they are not going to bloom anything, for a very long time, except bacteria.