Green dust looks like some one left a green chalky film on your tank walls. Doesn't cloud up your water to the naked eye unless you scrape it off the walls. Seems to take 4 to 5 days after being removed before it builds up enough to be seen on the sides. I have been fighting it for a few weeks now with mixed results.
I am using papertowels to wipe the GD off, I do a large water change at the same time and I run a UV for a few hours afterwards. I don't do water changes daily but I will try to do harass the algae more often than I have.
All three of my different type of snails seem to ignore it. My Bristlenose pleco and oto's seem to lightly snack on it. But other than making lighter patterns in the green they don't clean it to the glass.
I got it for a few weeks when I first started on the EI regimen. I'm not sure what spurred it on. I do know that my nitrates were aroun 40ppm and phosphates were around 4ppm, I also went a little crazy with the iron dosing for a couple of weeks. I wish now I had done a control to try and remove it but I didn't. I finally get rid of it but hell if I know what the catalyst was.
Here are some of the things I did.
I decreased the photo period from 12hrs to 10 hrs.
Ran the UV after scraping the stuff off.
lowered nitrates to 10ppm
lowered phosphates to 1.5ppm
I think it might have been brought on by some jobes sticks that had been stirred up during a major replanting. I think all the jobes are gone now, which might be the main reason why it finally disappeared.
I got this stuff last year and it drove me nuts for about two months.
I had increased my lighting from 2.35wpg to 2.85wpg. You wouldn't think this small increase would trigger something like green dust algae...
But it did. I tried everything.
I finally gave up and reduced the lighting back to 2.35wpg and it went away.
I'm pretty sure that at the time I did not have my fert levels correct (especially CO2) and that this combined with the extra light was the problem, not just the extra light. I mean some people are at 5+wpg and don't have this!
Now that my ferts are good, I may try increasing the lighting again...