weird algae growth pattern...

[ChicoRaton]

On my planted 55, I have a problem with brown algae growing on the rocks and glass. It doesn't grow on the plants any more since I cranked up the CO2 and lowered nutrient dosing. Anyway, on the glass, it grows on the bottom and up to a line 1/2 way up the tank glass. it's a very clearly defined line. very perplexing. Any idea what causes this?

 

[RTR]

Light level? FW diatoms are fairly low light.

 

[SnakeIce]

is that the line to where you lower the water when you do water changes? if you let the glass dry out it kills most of the diatoms/algae that is there. but the glass that is below the water line even if you scrub/scrape it off there will still be some surviveing that restores the eyesore film you get

 

[ChicoRaton]

light is 110w of PC. I think snakeice is right. it's about at the level I do my water changes to.