Instruct: Classify Amazon reviews into positive or negative sentiment
Query: works well, if you keep on top of it

These pads worked pretty well for us. It did take a couple weeks to notice a difference when we first started. The only trick is remembering to add additional pads before the one in there is used up so that you can maintain the clear water. You also will have to clean out the algae when you first start using them, as they inhibit the growth of new algae, but don't seem to do much harm to algae that 's already there. I still found them worth it. My pets drink that water, and I don't have to worry about toxic chemicals being ingested by them.