Ok that looks like what I had and let me tell you what I have done to try to get rid of it. I could not starve it out as suggested on this forum so the first time, I took everything out of the tank except for the gravel and bleached it. I took out the return tubes, suction tubes, driftwood (it ruined a beautiful piece of driftwood), real and fake plants, the only thing I didn't take out and bleach was the gravel and the eheim filter (only the intake and return tubes were bleached). Well this took care of the problem for like 2 days. I noticed a small amount on a few pieces of gravel so I tried to get them out...too late. That stuff started spreading again. I tried a 3 day blackout but it still continued to spread. It got on my new piece of driftwood so I took EVERYTHING out of the tank and bleached it this time...including the gravel. The only thing I did not bleach was again the eheim. If this stuff comes back this time then I am going to have to break down the eheim and completely re-cycle my tank. Most of my live plants did not survive the bleaching this time. I was much more aggressive about bleaching everything. I just did this second breakdown and bleaching this past weekend and so far, nothing is in the tank. I am keeping my fingers crossed.
I have read that you only get it by having an "infected" (meaning a piece that has been exposed to it) piece of decor or plant. In my case, it was just starting on a piece of driftwood that I bought from a store that was using it in their display tank.