Thank you so much for a thorough reply!
I didn't know all of what you said about nitrate processing bacteria. Thanks a lot. As well about the numbers. Now those talk to me. Those numbers would explain why the numbers didn't seem to move, especially when my test maxes out at 160.
Thankfully my skimmer is good, rated for 130/60heavy, and rock I have a lot for the tank size, but yeah, I bet not nearly enough for the load.
As to the fish, here's what I'd be willing to do lol. Please tell me if this would be sustainable for 4 months, with weekly water changes:
-Damsels all will be gone. They're food, and if not eaten in a few days, I"ll take em to my office tank and they'll be happily eaten there.
-Moonies as in Mono Argentus. They will go either in the mantis tank, or back to LFS. I don't like their personalities, or perhaps lack thereof.
+/-tangs are about 2 inches currently, you think they'd be thaaat bad for the next 4 months? I mean I can rehome the chocolate one once I see the chocolate on him. If they wont make it that long, then I'll part with them too, not too attached. Otherwise plan is to meet their adulthood in the big tank in 4 months.
+ Cowfish will be fine as far as space is concerned for 4 months until i set up the 525. He's still like 2.5". Right? I mean those minimum requirement sizes are for grown adults, long term housing, right?
+/-Foxface I could give up too. Not too attached, but he's still small, want to enjoy for a couple more months. He's 2-2.5"
-Firefish was eaten

solved that problem I guess.
+Batfish is small too. It's not the longnose subspecies that gets to 9.5 inches. Doesn't take up much real estate, and I keep him fed. I believe I can manage him for 4 months.
+Seahorses are all staying lol It either has to work or it has to work.
+Lionfish is staying for sure.
+Anthias I like. He looks fed and happy, it eats mysis and brine and pods that I fill up every week. Used to have 2 spotted and 1 ruby red dragonets up until a few days ago. They joined the firefish. If this guy survives, I wanna keep him.
+Leopards are eating very well all the mysis, brine and worms and all the bits of live food that they can get. All 3 are different kind, but I donno how it works out for them as far as genders and such, but they are peaceful. Honestly, if it stays as is between them, I'll keep all of them for the big tank.
The ones I have as +, do you think I can manage those for 4 months? Also, do you think they will be fine for 2-3 years in the 525L? I mean I'm willing to do the water changes, and even got an R/O unit, but I'm hoping to cut down my maintenance SIGNIFICANTLY when I switch to the larger tank soon.
Also, I don't mean to be asking you personally all these questions, but you brought up some detailed points that have always piqued my curiosity, but now it's more about some practical solutions. So anyone's input is greatly appreciated!