Updates.
My tank looks better than it ever has.
But I suppose I still "have dinos."
Every day I wring out, then FW rinse clean the filter floss strip that I have mounted in front of my biggest powerhead.
It's always ostreopsis that comes out, virtually nothing else - pure ostis.
So that's my daily dose to do experiments on. No sign of dinos anywhere else in the tank. I do have one corner with a little patch of cyano. I still have a massive amount of caulerpa and chaetomorpha in the tank. Not ready to remove it yet.
As for experiments, I repeated the iron B12 trial using a different B12 vitamin with different fillers than the other one.
Last time the control had very few dinos, B12 grew more, and Fe grew more than double the amount of others.
This time the B12 did worse than the control at growing dinos. It grew cyano and bacteria much more. I suspect much of the effect either way is fillers in the vitamin, going to stop testing B12 unless anyone knows of a pure b vitamin source.
The iron treatment again did by far the best at growing dinos. The dino population in the Fe was at least double that in the control or B12 every day for about a week. In the end, Fe had almost 3x dinos (ostreopsis) that the control did.
I feel pretty comfortable saying that in my tank with high levels of available N & P & light and tons of macroalgae, the low presence of iron limits the dino growth. (I'm sure it slows the algae growth too). To me it's not far fetched to think that it might happen in other healthy systems where algae growth keeps Fe low and keeps dino population growth below predation levels and out of sight.
If anyone knows of a method other than algae competition - faster hopefully - that can take iron down below biologically usable levels that might be an interesting thing to look into. Triton Detox looks intriguing. But remember we're talking about levels way below what Triton test (or any other easily available test) can detect.
That seems in Randy's wheelhouse but I haven't seen any posts of his about stripping Fe out of water, except to tell people don't do it.