Need some plant doctors advice Please

3 Bubba Kush HSO autoflowers aged 34 days
Indoor grow 1500W blurple(251draw) @ 18-24inches
Watering usually every 3-4 days with ~2L water when pots are light
Medium is Sunshine Mix#4 aggregate plus
Been Phing 6.5 in runoff was showing 6ph
2 pre flowering 1 flowering since last week
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Growth seems stalled slightly.. leaves looking somewhat droopy. Each plant slightly different. Seeing Yellowing, browning spots/tips on lower growth.. tp growth looked liike nute burn, but the yellowing seems to clear up mostly on top as they grow out.. need some advice? Over watering? Nute burn? Nute deficiency? Started with 1/8 nutes Green planet medi one 4-4-3 3 weeks ago, last feeding i went 1/4 strength. I have the bloom nutrients but havnt used yet.. GP Massive. Please help me understand whats happening before i move to correct. Thanks in advance peeps!

Looks like they might a bit overwatered, heat stressed or suffocating from lack of fresh air. if you truly let the medium dry out between waterings, I’d lean more towards heat stress and or ventilation because it’s 26C at the very bottom so higher up temps may be too high and I see mildew growing which is another sign of poor ventilation(first pic) and some other minor signs of pest infestation(second pic). I see some very minor signs of nute burn not bad tho. All or some of these factors are stressing your plants. If it were me, I’d watch temps & RH at day and night, increase ventilation and air circulation, spray insecticidal soap and neem oil every three days, allow medium to almost completely dry before watering, water with 130-250ppm 6.2-6.8ph water without ph adjusters preferably. good luck mate

Thanks for the reply.. The mould is actually some diatomaceous earth on that leaf.. my humidity hovers at 40 consistantly.. and temps never higher than 80, usually a deg or two below that. avg 23-27C. As for the lil hole in the leaves.. not sure what that could be.. i see no signs of pests, and i flick some DE around on the soil every third watering or so.. I saw an earwig in there once, and whacked him. As for air circ, i am using a 190CFM 4" exhausted to outdoors in a 32"x32"x63" tent,with a nylon over the intake just above ground level for cool fresh air. so should be more than enough.. Also a 6" clip fan, and a tower oscillator in the corner.. I do let the pots dry out before watering, till they feel TOO light lol.

Think i have figured it out.. red zoning the humidity/temp.. transpiration was screwed.. got it back up to 50% and dropped temp to 25.. 27 and 38-40% was not good

How did you whack the earwig? Did you take the cannoli?