I'm in agreement with both Waira and HM on this. The damage on your margins and possibly the tips looks a lot like your going through some wild P fluctuations.
You may want to search for a deal on the Oakton Eco2 tester. Usually you can find them for about $50. Mine has been going strong for over 3 years now

I started with the soil kits, arrrg! I never could get a decent reading.

The interveinal necrosis and stippling really looks like pest damage to me. I'm sure you have already, but I would check once more, especially on the underside of the leaves. You can even take a damp tissue and wipe the underside of a couple of leaves and look for any unwelcome guests.
If you wipe, though, only use one tissue per plant to avoid spreading anything around.
I'll take another look tonight, when my screen is bigger than a postage stamp