would you like to see what it did to an anubias as well?
Also I have absolutely no reason to lie about anything and that's what you pretty much just said
I'm not saying you are lying, what I'm saying is that Excel alone
in 5 ml per 55 gallon tank dose (every other day!) is not
killing fish and is not
killing anubias. This dose is way on the safe side. There are few plants that don't like Excel but anubias is not one of them (and in fact it is one of the hardiest plants to kill - some people even wash it in bleach to clean the algae). Come on, some people use Excel even with CRS. I personally was sometimes using up to twenty times
recommended dose to kill algae - without any negative effect on plants, fish and shrimp (bamboo and amano). Some fish in that tanks is usually considered pretty sensitive to chemicals - e.g. zebra loaches, chocolate gouramis, ottos.
I've no idea what have happened in your tank but the symptoms you've described point to breathing problems in your fish which may be caused by many "innocent" things that can easily go unnoticed: temperature got higher then usual, turned off canister filter for half a day and then simply turned it on, too much CO2 got injected into tank (if using CO2 injection), water circulation reduced because some pump broken / filter got clogged etc. - there are many small things that can easily fall into category "nothing really changed" from human POV but can affect fish.
I'm pretty sure that something else caused the problems you describe, something else happened that you've missed. I do understand, of course, that on your mind it is Excel and so you are afraid of its use.