When we opened our pool in the spring it appeared we had a rust spot. You can not sweep it or vacuum it away. Now we are getting many more scattered about. What is it and how do I treat? I have the suppllies super cal-shock and a clorinateor.

A friend told me they think it is the mustard algae. They had it and it was hard to get rid of. What to do?

I would recommend a professional water analysis to check for minerals (mainly copper/iron), as they are a main source of staining. A quick test with a Vitamin C tablet on top of the stained area will tell you if it is a mineral or organic stain. If the Vitamin C tab removes it, there are stain removers available in larger quantities to treat the entire surface area. If Vitamin C does not work, it could be embedded mustard algae.