since i only have approx 26 gallons in there, i think the 10 gallon i did is a pretty good amount and like you i think would only be a temp sollution.
main reason for doing the change is because i wanted to really blow the junk out of the rock and it needed to be in salt water so why not.
granted i have pods, amphipods, but not much else.
that's what i am having a hard time with. it's not like i put 6 fish in there right away and overtaxing the system. other than feeding a few pellets every other day for my cleaner and snails i have 0 going on.
i would think that the way i am doing it would give it time to form a nice little cycle.
rocks have some green algae with some having small green hair.
no diatoms left but sand has some detritus.
at midnight with lights out tank looks crystal clear, but by morning have a pollen haze devoloping and a little bit of white cloudiness.
water is showing 0 tds from my meter on ro/di. 36 going in and 0 going out.
i may try blowing the rocks out again in hopes to get even more out, but i would be lying if i said i wasn't getting a bit frustrated.
just put 1/4 cup rowa phos, 1/2 cup seachem's matrix carbon and new polyfilter in this 10 gallon change in hopes to fight phosphates if the rock is loaded with them.
A large WC might help but it may only be temporary. Since you are moving the tank for carpet you may want to give it a try but your shrimp and CUC aren't gonna like it unless you get that water close and you acclimate them (wanted to mention just in case). I know I sound like a broken record but I just have to think it has to do with a lack of diversity. Pods, feather dusters, micro stars and other bacteria all play a role in the ocean and I have to think this diversity becomes even more important in our little glass boxes.
What I am having a hard time with is the longevity. These bacteria need a food source so where is that coming from that is allowing them to survive and repopulate for this long?
How are the rocks and sand looking these days? Still seeing and green/brown algae or diatom frustules? Water any clearer with lights on/off? Sticking to a regular water change schedule and have you verified the water source has a zero TDS reading? Is the water still just cloudy white or is there any color to the cloud?
Leaning towards something buried deep in one of your rocks fueling this thing. Maybe get a hold of a really powerful pump or powerhead and just blow the daylights out it in some buckets of SW when you move the tank.