Sorry to hear.
OP, one thing you wrote in post #6 stands out to me.
The tank is an AIO.
Has it always been this tank? Could it be something with this tank? Chemical? , stability with AIO?
Maybe break out the 90?
100% Agree with moving on to the 90 with a sump. AIOs, although low barrier to entry, much more limited and unforgiving than higher volume sumped aquarium setups.
Broke down the tank tonight. Soaked all the pumps and what not. I don't normally use vinegar but I had some 30% and I was out of citric acid. When I got to the mp10 I noticed the magnet was swollen and rusty. Hard to say how long that's been that way.
Sounds like a great time to jump ship!
There are significant benefits you'll see if you've never ran a tank with a sump.
Better and more efficient filtration options.
Higher stability from larger water volume.
A cabinet you can store all your equipment and goodies in.
Availability of space to run all sorts of systems.
If you don't already have it, make sure you get these pieces of equipment. Some are no brain er but others are just significant improvements to quality of life.
Heater and external temperature controller.
Properly sized protein skimmer. (my 120 rated skimmer handles 3 tangs, 3 clowns, and 1 foxface beautifully)
Eheim or other auto feeder if your fish eat flake/pellets.
Auto top off. (I like avast but any will do)
Truth be told, I think most of your problems occurred due to the difficulty of keeping water stable in an AIO and less about the specific state of your parameters. The equipment available in AIOs pale in comparison to the equipment available for sumped systems. And AIO controls often are able to affect the tank so quick that it could be harming the tank in the process.
You may find that you do not need as many controls as you implemented in AIO. In my setup, I have an ATO, Protein skimmer, Calcium reactor, Kalkwasser reactor, and ATS. So far the protein skimmer is handling most of the legwork on nutrient removal and the ATS is acting as a buffer.