vacuum

I would like opinions from people that have used the battery operated eheim pro gravel vacuum, is it worth the money?Is it to strong for sand substrate?

I've noticed at the bottom of my tank, there is waste building up around my rocks on top of the sand. Does anyone recommend to take the rocks out every so often to clean the sand bed? How often if so? There is two mounds of rocks so I could do one side and then 2-3 weeks later do the other side..