i had this same issue with the same medium as you. one of my problems was too small pot. so i transplanted in 5 gallon. next is have you checked you run off ph???? i bet that is the main problem rather than the pot size but when roots tend to hit bottom, the tips curl down, ph makes the leave curl like an upside down canoe. when plants go into flowering stage the soil tends to get salty and acidic with ffof. you gotta do a light flush, check your ph runoff and raise it. check it, i bet your going to get a low ph.
cigarettes42 Reviewed by cigarettes42 on . Curling Day 18 flowering. 400W HPS on first pic with curling. 3 gal pots soil grow. T5's are not curling the HPS is. Any ideas? All nutrients are the same for HPS and T5's The only difference is the amount of fan, which could contribute to cold or the HPS. Any ideas? Rating: 5