Cleaning stones on trays without harming plants

[ladyslipper]

Hi guys, I have decided to put my plants (mostly phals) on little rocks in trays in my grow area. My question is, even if I am using RO water, the area should be cleaned even once and awhile. At least that was what I thought. How can I clean the rocks of algae for example without removing all the plants and pretty much taking the stand apart? I was hoping something I could pour into the rocks like water. I have all the plants on saucers so no one actually gets their bottoms wet from the stones. I would like something that would clean then evaporate.

Any ideas? I guess the other question is if I am using RO water, do I have to worry about little life forms growing on the rocks?

Kindest Regards, m