this really depends on the tank, is it glass or acrylic?
I do not recomend mag cleaners for acrylic tanks especialy for those with sand beds, it only takes a second to scratch your tank if a piece of sand gets in the cleaning pad. Mag cleaners are nice and easy but for an acrylic tank you really must take precaution. if you do use a mag cleaner on a acrylic tank I strongly recomend changing the cleaning pad after every use and stay completly away from the bottom of the tank to ensure you do not get any debris in the cleaning pad.
Yes I agree. Akso do not leave it in the tank. Take it out and wash it and leave it out of the tank untill you want to clean it again. Also another great tool for acrylic tans is the Kent scraper with the acyrlic blade.