Your res temp is pretty warm. How do your roots look? 75 is the beginning of the danger zone for res temps, so if you aren't providing tons of air, the roots will rot and that will stifle your bud production for sure. Been there many times myself .

Also, if your res temp is 75, your air temp is probably pretty high as well, which can cause slowed growth. I would get a thermometer/hygrometer combo, they are around $30.

Other than that your PPM is pretty high as I already said, I'd lower to around 800 for a week and see if they bounce back.

Good luck!