Ceramic Pipes for keeping water butt clean

Has anyone tried those little bags of ceramic pipes to keep their water butt clean? Do they work? I would prefer to try them above tipping chemicals in the water, but want to know if they are just a gimmick

Water butts will stay clean if you have a good lid on them to keep out the light and refrain from dipping dirty watering cans in them.

I've used ceramic tubes in my bird bath. I think they worked for a while but they get covered in gunk eventually. Haven't bothered since.

I've also seen something that just looks like a silver coin advertised in the Lakeland catalogue. 

I've never tried either though.

I thought that with the really well fitting lid that ours came with, nothing much can get in & as it's black it keeps sun out which is probably what causes algae etc. The water that comes out of the tap below always seems okay. 

Many thanks for the advice. I think my problem clearly stems from the fact that the water butt I inherited has no lid. I shall fashion one out of some old scraps of wood I have lying around, give it a good old clean out, and from what you are saying, I would hope that solves matters.

Thanks again