Im not promoting or anything lah. But im using cuckoo at home, outdoor filter. Before filter my upstairs water tank at the surface full of teh tarik. After cleaning the tank and fix the filter, even after 3 years, i didnt see one brown spots on the tank surface, its super clean. So this is really good thing and it really works. Indoor i dont really give a fark but outdoor is very important because thats the water goes to ur tank and my house the tank is the water that supplies to everywhere. So im pretty satisfied.