I use it upon the advice of DJW, but my tap water has very little mineral content. It gets a little pricey for my taste, but my discus have no pits in their face, and I believe having all the right minerals is the main reason. Some say that discus get most of their minerals through their food, but I can't say conclusively one way or another. I am operating under the "ain't broke, don't fix it" model.