...has been steadily growing over the past couple of weeks. It's not taken over the tank, as such, just a few leaves here and there and a patch on the rear glass, but I know I need to do something about this real soon. The stuff is a red-brown colour and seems to wipe off fairly easily by hand. Not that that makes me any more secure feeling... Any suggestions? I've introduced a "siesta" period, for an hour, right in middle of the day. I now have a 4.5 on/1 off/4.5 on light cycle. The only fert I have is an LPS bottle of "Plant Food", as well as the obligatory DIY Co2. The tank is 70L and not overstocked at all.