There's a chance that you might have low levels of dinoflagellates in the tank, though I don't see any obvious signs in your pics, particularly because your tank is pretty new and will have a few stages of the uglies.
I'm relaying my current situation because it explains why I suggested the possibility of dinos.
Given that you don't have an obvious smoking gun at this point, I'd consider sending out an ICP test for like $40 as I think that would be more cost effective than buying several test kits for various elements that you probably won't use again. If that doesn't produce a smoking gun, it's probably worth spending the money on a microscope. I got an
Amscope MC 150, currently $84 on Amazon, but any decent high school quality microscope will provide all you need for dinos, and likely anything reef hobby related. Honestly, if you have the extra cash laying around, a microscope is handy to have around and might be worth just grabbing anyway. I found that I enjoy looking at random stuff from my tank and it can help with identifying some of the smaller pests we come across.
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