Water changes are always better than adding chemicals to clear the water, doing such is just delaying the problem imo. What rocks did you add, and did you prerinse them untill the water you were washing them with ran clear. Even if the bag says thier prerinsed, it doesn't mean crap, your still best off rinsing before adding. Also as said, it could be algae, if its more on the glass than the actual water itself, there most likely lies your problem.
Also if none of this is the problem, then your best off answering elevatethis's question, as that could be the source too.