I'm curious about your lithium reading being within the normal range... as myself and others I know had extremely high lithium when we had our tanks tested. ** I will add mine was over 1000... but my tank never looked better. I think the consensus was that it was present in the various salt mixes, as well as 2 part. So my question for you is what salt are you using and are you dosing 2 part or on a calcium reactor?
I dose with a calcium reactor and I use two little fishes coral media (REBORN). I saw too much unusual foreign material in ARM media so I don't use it. My salt mix changes over time because like many others, I am searching for that really awesome, reliable, consistent salt. I used IO for a short while but didn't like adding muriatic acid to lower alk. I use to use red sea salt (the one in the blue bucket not Coral Pro) because the alkalinity was around 8. I also tried D-d Salt because alk was also around 8 but red sea and d-d left smudge on the side of my saltwater storage tank. I have been using Tropic Marin for about a year now. I used one bucket of Aquaforest Reef salt (not the probiotic) and it was fine. I just bought a box of Fritz's RPM to try. I like salt mixes that give me a dKh of around 8 which is where I keep my tank. But I guess you can tell, that I have not been loyal to only one salt mix.
Oh and i should add that i change 10-15% water weekly. And if anything looks goofy in the tank like something just not happy, then I do a 25% water change over a couple days or three. If concerned after that, I do the same thing the following week. I test alk and nitrate usually twice a week, sometimes more frequently and very rarely less frequently. I like visually observing sps looking happy, but I also want to verify that alk and nitrates are stable. I think corals can look happy while deteriorating or fluctuating parameter changes are taking place until one day the tank transitions from looking happy to crash. I am most comfortable when the tank looks happy
and parameters are stable