I am no fish expert, but logic dictates that you have just had a hugely stressfull incident in your tank, effects are bound to be collateral (sp?)!
Besides the macrolife taking a serious culling, believe me your microbiota will have all taken a severe knock. Have you checked for ammonia and nitrite? As
@RiaanP mentioned on ur other thread, 12 hours of Current running through a soup containing every known element.... The science gets way to complicating for a peabrain like me to dare think about... The parameters we measure are just the tip of the iceberg.
You are sitting in a catch 22 here:
Reaching and maintaining parameter stability is paramount but at the same time you gotta get things back on track... Really a tough one... Good move on the water changes, but not too big too often. Also, a good quality carbon would help. Awesome move on the addition of stabiliy to get the microbiota back on track..
The important thing is to not panick and start taking drastic action and just as important is to not throw in the towel..
Regarding the elevated po4, dont go add a litre if gfh now and strip it out, its a good thing its there... Wait for things to stabilise and then slowly bring it down.
The reality is you are likely going to lose another fish or more.. I really hope you dont..
With carefull TLC your tank will recover, in a few years this will be put down to school fees..