Need help with potential fungi/bacterial problem

Hey guys, first post here. I can't seem to find anything online. SWIM has an inexpensive hydroponic grow room set up, and thinks he might have a mold problem. A white growth of some sort has began to grow on the rocks used in the grow room (they are essentially crushed up brick). The only areas where the growth is present appears to be on the tops of the rocks.

Can provide pictures if necessary. Is this really dangerous to the plants? They seem to be growing quite well. I have read that this could simply be nutrient buildup on the rocks, but I don't think so, since not all of them are entirely submerged in the water. Can a water/bleach spray be used on the rocks without harming the plants?

no

no bleach, youd be better off with a mild vinegar spray

and becuase of capilary action adhesion and repulsion it is possible to get nutrient buildup, usually doesnt happen at the correct ph levels, but can given the right conditions.

look closely at it, it its nute buildup it should be in the form of insoluble mineral salts, as such they would look crystaline under scrutiny, and if disturbed should fall roughly down.

wheras mold will spore and drift with the wind