as long as the parameters are in check, is that my biggest concern?
from the parameters in the OP, Magnesium is the only one that seems to have dropped in the two week time frame. if the parameters change, other than Nitrates and Phosphates, what other parameters could cause me problems if they were to decrease?
So I started roughly 6 months ago, started with live rock and sand, started with a redsea tank that I swapped out to a waterbox (long story cut short here).
Except for the first month, I've not done water changes except to adjust salinity... Ie, in my new 230.6, I've done 1/2 dozen 5 gallon changes with extremely high salinity water, to bring my salinity up from 1.021 to 1.026 (it got way too low during the tank migration for some reason).
You seem to have a good system in place for water changes. I don't. And I really find them to be chore-like, so when I started this journey I knew I would dose something. So I dose All for Reef both to maintain ALK and to add back in trace elements, and I pretty much don't do water changes.
Adding a little more to this, post-tank migration my nutrients bottomed out. Don't know why. I then had my first real nuisance algae issue, dinos. I had to dose N&P as well as some bacteria, and I'm on the mend with the dinos. My HG Torch instantly liked the increased nutrients, the other hammers are coming aorund to being back to normal, and the nuisance algae is almost gone.
And I just added a big cleanup crew from ReefCleaners.
Just another way to skin this cat so to speak.
I go back to dirty water..... I'd test N&P before and after your water changes... Before is easy, after I'd wait a day. If you get markedly lower N&P post water change I think you'll have your answer.
I also believe in the thought that if you can grow anything, youre going to grow algae. I've read that there's some ULTRA low nutrient systems that don't, but I suspect those are SPS tanks.