It's a micronutrient deficiency, common when you use RO water... Mainly calcium but other minerals like iron and magnesium are taken out of the water with an RO filter.
They can be supplemented back in with more micro from a three part nutrient regimen...
Or you could stop using RO water, and the minerals won't be filtered out.
It depends on what the situation is...
If you can aquire some bat or seabird guano, or fish emulsions, they have lots of benificial nutrients, compost food waste and animal manure for a good fertillizer...
Make sure you have a good soil mixture, plenty of sand for drainage, if the soil is mostly clay and rocks, you might have to bring in more topsoil...
There is so much you could do, but only so much I can help you with... I can't write a novel.
Do some research, there's plenty of info out there, you already know the proper pH level and are using an RO filter, so I call bullshit on the rest of your story...
Add more micro, if it's only a few leaves and the plant is mature and growing well, it's nothing to worry about, snip them off, they won't recover...
It's also common for a plant to drop fan leaves as the branches get larger, don't worry about it, it's totally natural.