Problem with 4 plants of 21.

You've got 21 plants in your tent?! 21!! There's not going to be enough air flow in there for good healthy development, seriously. These 4 likely have some root issues (and you can bet it's developing in some others)... and your humidity is way WAY too high... they're not getting a chance to dry out. Let's see, if this was my grow, what would I be doing ... I'd haul those 4 out of the tent and try to examine the roots first of all to make sure root rot hasn't begun... and then I'd leave them out of the tent with a fan blowing directly on the pots/soil (I hope they're in fabric pots?!) ... and I would be making plans asap to get another couple of tents - a LOT more tents ... but if that's not possible, I'd be choosing the strongest of the 21 to keep going and just forgetting about the rest. To figure out how many to keep, the key question would be how big your tent is - my tent is only 2x4 and I have no real sense of the capacity of different sized tents ... but in a 2x4, the max number of plants I have is 3 - and that's crowded if grown well... If I want good space to allow for a good scrog or heavy LST work, I would only grow 2 plants.... so basically figure on 2 square feet per plant.... with 21 plants, that would require a tent or room that has 42 square feet... so if you have a 4'x8' tent, you could conceivably grow all 21 plants in it if you had good extraction and air movement below the canopy... but it would be better/more manageable if you pitched the four problems... Good luck...