Once it's on them, it can be TOUGH to get off. Species with tender leaves are subject to damage if it's caked on enough to require some scrubbing. I use a paper towel dipped in white vinegar and it seems to take spots off in most cases. But I've gotten plants from the local university where they are under a mister that mists them several times a day and it can be brutal getting that long-term build-up off.

I use RO water in my spray bottles, but even better (if you have really hard water) would be to use distilled. You can still add some VF-11 or fertilizer to the water, but I wouldn't add any SuperThrive since it's pure minerals. I used to add it to my spray bottles and they would eventually become encrusted, whereas this has never happened with VF-11.

Denise in Omaha

I've used milk before, which I read somewhere was good, but there's still some gentle rubbing involved. People say lemon or apple cider vinegar solutions also work. Maybe even aloe juice works - I use it as a hair clarifier.

I spray my plants with RO water now, but I believe I stopped seeing spots after I started spraying them periodically with soapy water. I do it to stay ahead of the game with pests, but it has the side benefit of shiny clean leaves. I didn't scrub them - but they do get pretty drenched. Idk that I'd advise doing that all the time if you don't have any pests though. I'm trying to minimize the use of detergents on my own body and it seems like it would adversely affect natural plant balances too.