A few years ago Baquacil came out with "CDX" - a liquid that is added directly to the skimmer following the oxidizer. It is reported to work really well with avoiding the white water mold problem that is common to biguanide pools. The chemical in the product is apparently polyether diol. It is also supposed to help maintain the oxidizer level. A friend of mine said he has been using it faithfully for the last few years and has had no water problems, so I just started using it as well. There used to be a product called "Assist" that worked great to get rid of water mold, but it was discontinued a few years ago.