Thank you!

How much? How do I add it? Just dump it in the water? Put it in the
filter? I have dolomite lime in the filter. Will it mix okay with
that?

Where do I get it? Drug store? Is that the same as activated
charcoal?

Thanks so much.

Joan, worried about her fishies

Try adding some activated carbon. Something is telling me that it may be
some kind of poisoning. It may be low level, but carbon will remove the
poisons. There doesn't appear to be any other explanation that hits me,
based on the information you have posted.