I agree with Sunil. You need a jar test to determine if your water chemistry still needs correction due to suspended clay, OR if you water is murky due to your organisms stirring up the sediment.

Channel cats are not "notorious" sediment stirrers, but they COULD be causing your problem in your very small pond.

Here is a link to an old post on that topic. (Bill Cody gives a long answer, and he IS an expert.)

Channel Cats Stirring Up Sediment