"Growing in coco+perlite is hydro"
That isn't necessarily hydro, it can be just soilless. It depends on the way the watering system, if any, is set up.
You can over water in any application. The key to not over watering is knowing and understanding your setup and then aeration of your water/solution.
"i always thought hydro is when they r in those cubes and r being flooded several times a day" This is one type of hydro.
That Girl: if you have your plants in coco with no watering system, then you are considered soilless, and you would treat the setup just a little different than hydro, which would be if you any kind of constant watering system connected to a soilless mix. You could literally take plants in soilless that are in pots and set them inside of something to catch the water and drain it away from the medium and then have a reservoir that is connected to the pots so that it waters them periodically, and you would have a hydro setup. If you just let the water run down a drain or out into the yard even, that would be a hydro, drain-to-waste. If you take that same setup and capture the water that drains out of the plants and returns it to the reservoir, you would have a hydro, recirculation setup.
With you being in all coco/pearlite, I would be willing to bet that you are having PH issues combined with cal/mag deficiency. And it is possible that the PH is being pulled down by the coco to the point that it has been squeezing the nitrogen from getting to the plant in the amounts needed.
The ventilation not being on will certainly have a serious effect on them.