Sounds like you've got iron in the water -- and the Walmart stain / scale is one of the weaker ones. But, without knowing your chlorine & pH levels, I'm sort of guessing.

Lime green and clear, with NO slimy feel to the vinyl walls is NOT algae. It's probably metal.

You need a testkit; at least a cheap OTO / phenol red one, and you need to tell us what you've got in the pool. You also need to run your filter 24/7. Doing so with a tab in the skimmer will help remove metals.