I've been reading this forum for quite awhile, always intending on building my own scrubber. I have a relatively small setup compared to a lot of you (36 bow reef, with a 10 gal refugium), and limited space to set up any kind of ATS. I found an old hang on the back filter with pretty wide return, and was able to shape the plastic canvas to contour the lines of the outflow of the filter so that the bottom part of the canvas actually hangs in the refugium - the total size of it is 3x5 inches, but only one side. I did this several weeks ago, and have had great results - not a complete drop in nitrates yet, but getting there. I also have a very healthy growth of green hair on the canvas. What prompted me to post here is that today I noticed an almost black (could have been very dark green) film covering a lot of the mature GHA. It wasn't slimy, the GHA underneath it was still green and not coming off the screen easily. Any ideas as to what this could be? I currently have it lit 9 hours per night with a 50 watt halogen bulb in the warm range.
I have already cleaned the canvas, but if this happens again I will post pictures - I've been having to clean half of it at a time about every 5 days.