Could be a few different reason , could be your tank still needs to go threw and finish its cycle , not enough flow in that area , bulbs in lights are old .
well first off its not algae so no not the lights no not the flow and no its not the cycle the red slime is diotoms coming from your water source get ro water but this can still happen with ro we all fight it man it wont spread just get a Turkey baster and blow it off the rock and the grab as much of it as you can i always get it in the spring idk y but only in the spring with my ro water ... good luck
thanks fishit i am useing ro water so i wasnt sure why i was gettin it but its good to know its not gonna be a huge problem, i have been useing a turkey baster to get rid of it works like a charm.
Ya google it there's a good article on about .com said not actualy algae and does not grow it is setled out of the water just vacum it up not a proble coused by phosphates and perhaps kalswasher