Following up to my prior post with more observations, info from an ICP test, and microscope identification of what I am dealing with in my tank.
I bought a microscope and had a positive ID of LCA dinos (on sand bed) and chrysophates (rocks and back wall).
My ICP test came back with the following warnings (everything else was within acceptable ranges):
I think I've figured out where the Tin may have been coming from, but no idea where the Mercury is coming from (no broken thermometers or any other sources I can think of). I've tested my tap, rodi and tank water with test strips that check for Mercury and they all read 0. I've started using Brightwell Purit to help remove heavy metals and will send in a new ICP test in a couple of weeks to verify.
Trace elements were low, so I started dosing Red Sea Trace Colors A (Iodine, Bromine, Florine) and that seems to have some positive effect on my duncans (they've been closed up for months, but now I see them starting to open up a bit when the lights go out). I'm also switching my salt mix from NeoMarine to Red Sea blue bucket to see if that helps with trace elements. Will resume normal water changes again.
After increasing my NoPox dosage to the 4 week amount for a couple of weeks (maintaining MB7 daily dosage and keeping Nitrate and Phosphate levels up), I have not seen any noticeable difference in dinos. There was a large increase in chrysophates though. I also started getting a pink slime bacterial bloom in my sump, which I've seen before when the NoPox dosage was increased.
At this point I don't feel like this approach has worked in my situation with LCA. I'm going to slowly back off on the NoPox dosage (to get to a non pink slime dose), and keep up with the MB7 dose. I'll let the Purit reactor run for a couple more weeks to hopefully resolve the mercury/tin issue, then do another ICP test. Manual removal of chrysophates as often as necessary and siphon out LCA from the sand bed through 5micron socks. If the dino situation doesn't improve after the ICP test comes back (hopefully with better results) I will stop the Purit reactor and begin the silicate dosing approach to create a diatom bloom.