The "Sludge" Beneath my Hoods & Lights...

[ArtesiaWells]

I was doing my weekly 50% water change on my goldfish tank today, and noticed sticky, gangly "things" hanging from the underside of the fluorescent light housing beneath the hoods...it turned out to be, when I wiped it with a paper towel, nasty, thick brown goop/sludge that was all over the right hood and light housing and some of the plastic edges of the hood's underside....curiously, the left side didn't have much of this stuff on it, if at all...

The side with the sludge is the side of the tank housing the AquaClear 110, but I'm not sure if that means anything or not; anyway, I wiped it all away and wiped down the inside glass, as far as I could go before hitting water surface after I removed the 30 gallons, to remove the biofilm and debris build up...but I was wondering...what IS this stuff that was on the underside of my hoods? Was it beneficial bacteria somehow gathering up there? Is it just massive amounts of thick biofilm? As I said, it came off on the paper towel as a gloopy, really thick brown sludge...

 

[JadeGreen]

Not that I'm an expert, but it sounds like some moisture from evaporation allowed some brown algae to buildup.

 

[TOMatt]

I wiped all that off the underside of my hoods too. If it's the same as what I had, it's algae that's there because of the evaporated moisture.

 

[ArtesiaWells]

Thank you, both, for your replies; much appreciated!

So, am I to take it this is just "algae sludge" from evaporation? I do notice that since wiping down the light housings inside these hoods, the right side of the tank is lit up much more clearly and with more "pure white" from the fluorescent lamps, while the left side -- even though I wiped it down too -- seems to be exhibiting a dimmer, more "yellowish" tint to the light, so when you look at the tank head on, you can see where it looks like as if one side of the tank is lit in a bright fluorescent white and the other in a dimmer, more incadescent-looking yellowish tint...I'll have to try wiping the left side down better again, but I just found it strange that the algae buildup on the underside of the lamp housings would create THAT kind of "fog" to allow the lights to appear "dimmer" than they should...