I've been thinking more. When you say "normal lighting" just what do you mean? You need quite strong lighting to grow even corraline algae. Without, your live rock will be pretty much useless for filtration purposes. But if you have sufficient wattage (see GL's articles at the top of this forum), look again on the glass. If these are purplish, and are infinitesimally thin (the brittle stars will be noticably with bodies -- what I'm talking about is essentially and entirely smooth with the glass) then what's happening is corraline algae is growing on the glass.
This is hard to get off -- I've had no success with the magfloat magnets. I use a stainless stell putty knife every few weeks on the front and side of the glass that I look through (I don't worry about the back or the other side -- depending on the placement of your tank you may care about all sides) and vigorously scrape off any buildup.
Once you get critters ... snails, crabs, whatever you prefer -- you may have less of this growth.
While a bummer on the glass if it is indeed corraline algae that's a great sign, and depending on how live your rock is, I'd try and scrape it off the glass gently and transplant it to the rocks ... that's where you want it!
Pics would help to know for sure what's going on....
ions?
