Hm... well, you have left me seriously scratching my head and saying, "What the fuck?" Which is totally not helpful.
You don't think it's a cal/mag problem?
I'm messing around... And I shouldn't be... So helpful words...
Gnats live for 3 weeks before flying out. Thus you've got at least 3 times as many in the soil than you do outside. Add to that you've got several generations of them living in one apartment. Can you imagine living with your in-laws with 3 generations of kids running around? And there's no plumbing really either. Just some guy that dumps liquid down far too often drowning all the work the root zone has done trying to recover from the infestation. Bug shit all over the place. Bacteria infections galore too no doubt.
So aside from all that and I hope I didn't offend you. Just super high right now... Finally.
Rx...
OG Biowar tea. All three packs. Three consecutive feedings. No nutrients in between. Follow up with a strong enzyme. And foliar feed daily until back on track. But make sure to let the soil dry.
If you don't know when to water/feed wait for them to droop and show that they need water/feed. Then next time do it one day sooner. You can always get turgor pressure back but you can't drain the soil of excess liquid. I've seen guys wring it out... Doesn't work.