Help!

We started out doing great. High humidity (75-80%) temperature around 75. Plants loved it.

Turned on carbon filter exhaust fan setup and humidity dropped to 40% and my plants started wilting. Got a humidifier so for the past week it's been 75% humidity around 75 degrees. Plants won't come back.

They also have a deficiency that WAS phosphorus and I was treating it now it's just idk.

Not overwatered I think because I feed maybe every 3 days or more because of moist soil. Not underwatered for the same reason since I wait till it gets dry. Help.

It's highly unlikely you had a phosphorus deficiency and whatever treatment you used likely made things worse. How are you watering? Are you watering until slight runoff and is the soil actually getting watered all the way through? You don't provide enough info like type of soil, what you've been feeding, etc... Those plants are in pretty bad shape. I don't think throwing products at them will fix the problems. I'd water those with half strength nutrients really good to make sure the entire pot is watered and that there are no dry spots in the soil. They look stressed from overfeeding.

Whats the temp in the tent

And while you are in there, cut or roll the sides of those pots down. #1 most common thing I see is people leaving space to the top of their pot, destroying the air flow around the bottom of their plants.

Not your only problem here (obviously, your worst one looks pretty level), but it certainly isn't helping