I've got Chelated Calcium:

https://i.imgur.com/l01SxZJ.jpg

https://i.imgur.com/3QJC34l.jpg

Could I use that do you think?

Not likely to do what you want to do, which is to raise the pH. I think you really want something inorganic - strong base tied to weak acid. (corrected, had it backwards)You could see what that chelated Ca does to pH of some water, but the main point of that one is to tie up the calcium so it doesn't precipitate in the presence of sulfate, etc. So depending on how it is bound, the calcium may not be doing what you want.

I think I'll pH test several different bottled waters tomorrow, if one is 7 or above that may be the way to go ....

Thank you so much for all your help.

Even close to neutral should be fine. I had never thought about it until ES brought it up... The stuff comes in a sprayer already mixed, to be connected to a hose. But my tap water is around pH 7.8 because it's loaded with calcium. I do also have some BT concentrate that I can mix up in small quantities. The stuff works. (Spinosad is just a synthetic version of the active "ingredient", I think the real product with actual bacilli works better.)

Spinosad isn’t related to Bt. It’s similar in that it’s a naturally derived biological substance, but they’re not the same thing. Bt has residual effectiveness for a couple days and spinosad can remain effective for a few weeks after application. Bt is highly effective for the target pests and is more pollinator-safe compared to spinosad, which will kill beneficials when it’s wet.

A thought with regard to pH adjustment... a lot depends on what is making the water so acidic. If it's organic acids (like from decaying organic matter) it may not take much because those tend to be pretty weak. If something else, then it may be more resistant. As dry as your climate is, probably not organic... volcanic, sulfur for instance?

It was Dimples who brought up the pH issue.

Oops. Sorry

All desalinated water on our island

Surprises me... I would expect desal water to be on the alkaline side. But what do I know?