Welcome back !
How about instead of using skimmate you try something such as Seachem Stability or Microbacter7 ?
Throw a raw shrimp in the tank to rot until it starts to fall apart (week?) then remove it/repeat, or ghost feed - just add fish food every 3-5 days
And use one of the above or similar liquids at the same time.
Or you could pee in your tank
Just my $0.25