Hi, thanks for the pics :) We have had a few handfuls of people read the directions wrong by dosing 1ml per gallon instead of per 10 gallons with no issues, so believe this is not a overdose thing. The only time we have run into something like this, is when there are toxic dinos or toxins held within the algae's. This is super rare, but I can only assume there was some form of toxins held within the algae your tank had. The only other thing I can think of, would be low oxygen levels, which generally wouldn't happen so quickly. What do you run for filtrations on your tank?