If it's the brown rock face then do it real gentle as the coating comes off to reveal a less than desirable black look. Other varieties just use a soft toothbrush or the like
Agree with Doresy, do it cArefully, i cleaned my juwel rock background several times and had to remove it as the front layer started pealing off. I don't clean the back ground on my other tanks as my bristle nose plecs are keeping it very clean
Thanks for the replies, I hadn't thought about it getting damaged, I have been cleaning it with a suede brush? Just have to remove it when it gets too bad, I have probably done the damage already.