"David Ritter" wrote in message
...
I've noticed an oil like slick with a blue tint on the edge of the
water in
my power filter. It's a 10-20 gallon Whisper Filter that hangs on the
back
of the tank. I only see this substance on the water before the carbon
filter. I clean the filter system and it comes back within a week.
Any
thoughts?

--
DJR

Probably a protein layer. Planted tanks get this especially quickly.
Looks like an oil slick when viewed at the right angle. AFAIK, it's
essentially harmless, though some speculation has been made on it
interfering with re-oxygenization (which in your case makes no difference
as you only have a small patch of it). I think it's just a collection of
mostly organic compounds which has found a place where it will not be
stirred back into the water column, - AFAIK, harmless. hth

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