when you say you use 1/4 strength nutes, is it a 1/4 of the seedling dosage or a 1/4 of a normal veg dose? if your environment stays stable at those numbers i would guess its a nute issue. whether its too weak or the powder isn't mixing well in the water. what kind of water are you using? <200 ppm seems kinda low even for a small plant, but then again ive never touched those nutes... maybe call or email stealth and ask if the nutes should work for your style. some dont like to be bubbled, however im just thinkin out loud with that one, kinda unlikely but ya never know