Had a large amount of typing ready to go and the Internet dropped out :-\ I'll see if I can summarize.
Excel will certainly help you if you don't have co2, however co2 is one of the single most useful items in the planted tank arsenal. I agree your low kh and gh certainly might make for larger pH swings, but overall I think you might be OK. I have the opposite so I can't really judge. Lol. Do some research and see on your own.
If you're into building your own stuff you might try diy co2 just for something cheap. You'll see an improvement for sure. However you'll certainly be left wanting pressurized after a while. Lol.
What are those rocks you have? I saw some crystal like rocks similar to those at my lfs, was trying to think of a way to scape them. It looks nice though!
Sounds like your doing all you can to get rid of it! I've never had it myself so don't have much advice. From what I read it's like most parasites, heat up the water to speed up their life cycle and kill them with whatever will works (various treatments, maybe salt? Not sure...)
Good luck on the paintball tanks. I know it's made a difference for myself!
Very interesting agates wish we had some around here in Kansas lol. Too much limestone...