Mermaid Ashes, Krause springs looks like a good choice. It's about 20 miles away from Hamilton pool and very scenic, though I can't figure out how deep the water is. All the other places that look good are much further away, like the San Marcos river.

Zicoxite, depending on if I can make the meet up and if it's okay with whoever carpools with me I could probably swing by and pick you up. I'll get back to you on that.