First, is this pool considered concrete or plaster?
Second, the brown looks like rust, and the green looks like it was algae that ate through the concrete/plaster. Does this look like the case?
Lastly, should I use something to patch the small indentions that the algae, or whatever it was that ate through some of the plaster/concrete, caused to occur?
I am planning on using an epoxy heavy duty primer, followed by a heavy duty epoxy paint. It's a 2-step process sold as such.
Any help would be greatly appreciated... THANKS!!

Here are some images...






