Well I got my response from seachem.
Hello,
What size bottle of Excel do you have? We have discovered a misprint
on the 2L and 4L label. This could result in a overdose of Excel.
These caps are actually 10 ml not the 5 mL that is stated on the
label. This sounds like what could occur if that was the case.
I will get some products out to you to help clear up this problem and
compensate you for the trouble.
Apparently this product has some biocidal properties at higher dosages and the misprint caused me to overdose killing my nitrifying bacteria. Ammonia tested at the maximum the test kit will go this morning but the ammonia binding chemcals are still at work. NH3 form of ammonia is at 0 so thats good. Nitrite is going up showing that the bio-spira is working. I will do a 90% waterchange as soon as the 48 hours of the bio-spira is up to reduce levels. At least seachem recognizes the problems and is doing what they can to fix them. This event will probably save lots of other fish from similar problems. I still love their company and will buy their products just will verify dosages with them prior to dosing products which warn not to overdose.