Although a very long shot technically it is possible your releasing a "Mini Red Tide" on your tank when you clean the filter. Although the species Karenia brevis is a non-benthic planktonic swimmer excessive concentrations could be massing under the light, when you clean it most of the dinoflagellates could be released back into the tank poisoning the inhabitants.

There are hundreds of algae out there that can produce toxins, you never know with our little experiments :razz:.

My personal vote is for coincidence, look at the fish that died on you. An Achilles tang is the hardest tang to care for out there... period. How long was he established in the tank for prior to the incident? Anthias present a similar situation, although the Bartletts are more hardy than many out there it doesn't change the stats. Your third fish that died was a cleaner wrasse, was he eating frozen prior to the incidents? These fish also have horrible track records in captivity.

Would you please be as kind to post your system stats & maybe a few photos of the scrubber itself?

From what I've noticed is that skimmers are very sensitive to sudden changes in water conditions.

So when you turn off the scrubber, watch to see if the skimmer reacts. If nothing happens within a few min, I'd say its coincidence.

I'll try and get some more pics but I can assure you the fish were in pristine condition. All of them well established for months and eating very well with no signs of being unhealthy whatsoever. And then within 5 minutes, watching them change color from massive stress almost as if their scales were burning, breathing rapidly, eyes bulging out of their heads almost and then all of them slowing down and starting to die right in front of your face. It was horrifying. Everything looked like it would have been dead within an hour if I didn't act fast. I'm convinced it's something being released into the water from the algae. I just can't imagine what it could be that would cause such a fast reaction.

So you've removed it, right?? :)

Until I can get some answers, yes.

Just buy chance have u put a multi meter on your tank to check for stray current with pumps on and off

algae scrubber
 

what size tank do you have and how many fish.my algae stays on my screen when i remove it for cleaning so i can't see what you would be knocking into your tank.even if you bent your screen around-water is always running down the screen and would be constantly adding anything bad into your tank

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.

I haven't but wouldn't that bother everything when everything is running anyways?

That's exactly what I would assume too. I have a 180G with a 40G sump and I have 22 fish but half of them are smaller schooling fish so they don't have huge appetites.

That's my plan from now on. To be absolutely sure that any water discharged after the scrubber is taken offline is collected in a bucket. Right now I have it T'd off my return pump but I use a shutoff valve to stop the flow.

I'm pretty scared to even turn it back online again to be honest. I modified an aquafuge with pvc pipe and the mesh screen is the exact screen recommended by algaescrubbers.net (#7 from Michaels) so I can't see it being a problem with the setup releasing toxins into the water. The problem is my bioload is pretty high to not have it working too. I skim with a Bubble King 250, run carbon, biopellets and dose Prodibio Biodigest to keep the parameters in check and so far it's worked great given the number of fish I have. I also do 40G water changes every two weeks.