I have had in my tanks for decades, an algae that looks very much like Coralline algae from saltwater tanks. I have very (off the scale) hard well water. Alkalinity is high too. Other factors perfect. Very hard and scaly, have to use a razor blade and elbow grease to get it off. Thoughts on what it is? How to get rid of it?
Here's some pictures from a couple different tanks (33 long and 90 gal