Could the fish problems be because of the Excel? Didn't you say that is when you began to see problems? I have read that overdoses of Excel can sometimes affect some of the more sensitive fish/inverts.

But...you said you dosed 30ml. of excel in a 125gal. tank....I have used doses of half that - 12-15ml. - in my 29gal. tank with no effect on my shrimp.....so 30ml in a 125 gal. tank might not really be that much.

Just something to consider as well.

-Mike B-