I keep a close eye on my PO4 as well, how did you figure out you had an imbalance and how did you correct it?
My P04 was "high" and would not come down...water changes, GFO, Algae scrubber were in heavy rotation to try and bring down P04....but those actions also kept my N03 from being able to come up above 0.25ppm.
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Fed more, and added fish...grew all sorts of nuisance algae...kept changing the GFO and doing water changes....and ended up starving the LPS and both SPS & Chalice struggled with the high P04.
More food, more water changes, more starving corals...then cyano....then I dosed chemiclean to address the red slime and nuked the micro fauna...and a crash began

X marks the corals (in a pic prior to the hell began) that died
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Before the tank completely crashed, I began dosing NaN03 solution that would add 1ppm a day for 3days, then 2ppm a day for 2 days, then 5ppm every 2 or 3days, then things started to change.
I could now measure 0.5ppm to 1ppm N03 and the P04 started coming down...and then P04 started dropping quickly. In 3 weeks, with only 1 biweekly 10% water change, the ATS began producing and the P04 was down to 0.04...and N03 was up to 0.5 and stable. I took the GFO offline and kept dosing 5ppm NaN03 weekly for about another month and things stabilized. Corals started looking healthy again, P04 was 0.02 and N03 was 1 to 2ppm.
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That was Feb 2016....a year later N03 is stable (~1ppm) and P04 occasionally creeps up (from 0.02 to 0.06)...I have 13 fish in a 55g feeding the corals with poo...and my "battles" are now increasing ALK demand, raging coralline algae on acrylic and an aiptasia bloom....but I have happy corals
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Nitrate dosing isn't something you should have to do, but when N03 is lower than P04 it seems to have a place. That's my experience anyway~
P.S. I don't consider taking protein skimmers off line a good option. If there are minimal organics to remove, it won't remove anything...but it will aerate/oxygenate the water...which I think is underrated.