A little history. I checked my params today:
ALK - 9
Ca - 488
Mg - 1350
PO4 - 0.00 .... Hannah
N03 - < 1 ppm
This tank has been running since 2006.
I started a 35 gal cube last year. I bought dry rock from BRS for the 35. Rock cycled for 4 months before I started the 35 gal. Then in the tank for another 2 months before I got lights for the tank. I had some excess rock that I added to my main tank. This stuff immediately covered the new rock in my main tank. When I added lights to the 35 gallon tank all of the rocks in it became covered in this snot.
Now this stuff is spreading to adjacent rocks in my main tank. This video is from one of the rocks in my main tank. I have been siphoning it off about every other day but it just keeps coming back.