dying fish

I've lost a couple of clownfish lately and have only found one thing their deaths have in common. Both occurred within an hour of cleaning my screen. A couple of weeks ago, I cleaned the screen, rinsed it, and started it back up. My adult Occ. clown started swimming erratically and eventually swan under a rock and died. I had owned it for a year and a half (4 months in this tank). A few days ago, I picked up a juvi Clarkii in hopes that it would find a home in my Malu anemone (my Occ would have nothing to do with it). It went straight to the nem and seemed happy and healthy. Today I cleaned the screen. Upon restarting it, the clown started swimming erratically all over the tank (hadn't been 6 inches from the nem before this). Within 20 minutes it had swam under a rock and passed.

The tank is a 40 breeder with a 20 long sump. The screen is about 10x10 and is fed off of the return pump. I leave the powerheads in the tank running while I have the return pump off cleaning the screen. Lighting is two 23w cf lights on each side of the screen. It has been running since Feb. and the gha is finally starting to fill in. The only other fish in the tank are a Mandarin and a Randalli Goby (along with his tiger pistol). The tank also has a handful of soft and lps corals. Everything else seems to be fine.

Any ideas as to what is going on? Could cleaning the screen be releasing something toxic? Maybe the rinse before putting it back into service? Any ideas are appreciated. Thanks.

First time hearing of this. Sounds like something in your tap water, but even if so, it should not be enough to hurt. You should be removing the screen from the pipe, so any buildup in the pipe is cleaned out too.

The algae does not release anything bad... it's the same algae that grows in your tank that the fish eat.

how often do you clean your screen?

I clean my screen weekly. After I scrape it, I rinse in fresh water and then quick rinse with ro. It's the same way I clean pretty much anything that goes in the tank.

I think I may have lost my goby this time as well. I haven't seen him since about two hours after last nights cleaning, but he may just be hanging in a cave with his shrimp. I'll update tonight when the lights are on.

Thanks

when you clean, whats the color of your screen?
color of algae!

It had been a greenish slime for the longest time, but the gha is starting to fill in nicely now.

if it starts to appear yellow algae, clean that time!
the yellow algae produce FENOL(i'm brazilian, and i dont know how to write this in english..)
when you clean, be sure that in the screen you didnt let any yellow algae..

Yellow just means lack of iron. Nothing harmful is produced. It's the same algae that grows in your tank.

Could switching off the return pump while you're cleaning the screen be causing something odd to happen?

Seems unlikely but what else is there?

Co-incidence?

Finally have a little good news, the goby is fine.

I turn my return pump off everyday for feeding, so I don't think it's an issue.

Whatever the problem is only seems to affect more active fish. The Mandarin and the Goby seem to endure it without a problem. The way the clowns would dart around the tank before dying make me wonder if they weren't suffocating for some reason. I did notice the goby breathing a little hard last night, but I thought it was from the clown stressing him out. They normally stay on opposite ends of the tank, but when the clown was darting around, he lunged at the goby a couple of time freaking him out a little.

Please keep the ideas coming. It's frustrating having corals that are thriving while killing off my fish.

Thanks.