[tang daddy]

If it is infact your ATS, then perhaps you could in future have a bucket ready with the water that's returning back into your sump from your ATS go into the bucket for 1/2 a minute. What ever toxins that were released while removing the algae mesh would be caught on the return line in the bucket then also flushing the remaining water and remnants in the ATS and hose out.

Monocus was over when I cleaned my ATS mesh last week, because I run it in a 5g the whole bottom of the tank has algae and detritus settling from the low flow, I use my hand to scrape the bottom leaving loose bits behind, some of these bits make back into the sump and return to display when I turn my ATS back online. I've never had a problem losing fish although my return pump constantly runs, my ATS is fed from the chiller pump which is T'ed off and separate from the system.