How long do you take between waterings, i had some soil that took a week to dry, so i only had to water oncr every 7 days, even tho the top of the soil would be dry after a day or 2, maybe ur soil is just denser than you think.
Its just a guess, but try to not water for a while and check the weight of the pot, if you balance it a lil bit you can sort of feel if the center of the soil is still wet or not.
Maybe try pushing the lights a lil bit further away from the plant too.