Really Struggling with my LED grow, please help..

Hey rollitup community,

its about week 5 in my grow, and things aren't looking great. I'm growing 'Dinamed CBD Kush Autoflowering', purely for CBD bud. Growing under a 1500watt led (not output as i'm sure you all know, just stated wattage).

Yes im growing in a cupboard but the doors are always open and there's no ventilation issues, they get good fresh air from nearby ajar windows and have fans on them for circulation.

I'm growing in regular, garden shop compost (all i could seem to find during this pandemic to deliver to me), and am using the biobizz nutes (Grow, bloom, topmax, heaven, activera. The sickly looking leaves started a while ago, i had heard not to ph balance my water as was told the soil naturally buffers it, but things got worse so i got biobizz ph down to bring the water down from 7.8 to 6.5, have been using this ph balanced water the last few times and things are still getting worse with these leaves..

I had fungus gnats which i used Tanlin for (1 drop per 2L) in the last feed, have only used it once, am aware it only kills larvae so have sticky yellow paper around too.

Things have just gone wrong one after another, and i need to set this grow on the right path!

Please help me out here, i'm sure there are a bunch of experienced horticulturists that can tell me where im going wrong.. What is wrong with my plants!

Thanks a million in advance guys, attaching photos.

Apologies forgot to add that the light is phlizon brand, i have had these plants on 18/6 light cycle and im watering every 4 days, and being careful not to overwater and wait until the topsoil is dry before doing so (both for the plants health but also the gnats)

5 weeks of ph that high has stunted your plants and I'd bet they're overwatered too.
A cheapo moisture meter is essential in watering...you can't feel the moisture at the root with a finger...
Biobizz LM may buffer a bit but I always ph to 6.4-6.5...somebody misled you...
Your plants may recover a bit but....I'd drop a couple more seeds and get that ph under control for your next run.

damn, thanks man, will get a moisture meter. Let's hope they recover.. you think i should bring ph down to say 6 from here? Or is it a losing battle..