Chemipure is a carbon substitute. I have found it to be a very good filter additive that will keep the water fit for fish for up to 6 months before needing replacement. I personally use Chemipure as my only chemical filtration agent. I have had excellent results and I highly reccommend it. It's low cost and long life are just 2 of the high points for this product. I have had very good luck with all the fish in tanks with Chemipure in the filter. It might not stop algae from growing but it maintains healthy water that seems to keep diseases away. It's easy to use too. If you have a hang-on-the-back filter you just put the Chemipure bag in the place that regular carbon usually goes, then that's it, you don't have to worry about changing the stuff for another 6 months. If you're using an under gravel filter, you can just put the bag behind some decorations out of sight and not worry about your filter at all. The ug filter will take care of the biological and mechanical fitration and the chemipure will do the rest.