Curled\thinning leaves, light burn?

Alright, so I've got 2 Alien OG Kush females I've been growing from seed about 2 months now.

Fox Farm Ocean forest, and ... another fox farm (can't remember) soil mix 50/50ish.

Water is PH'd at 7.5 - except I've recently (2 weeks ago) started feeding them fish water from the aquarium... idk the PH, haven't checked but it's good for the fish.

Anyway, I've kept my light (HLG 100 Watt) pretty closeish (12-18 inches away) trying to keep these things from getting too tall while I'm trying to clone.

I've just started to notice the leaves are curling back, and maybe a little yellow from the center.

Just curious what the thoughts are out there - is it the light intensity?

I water about once every 6 days or so - when the soil feels REALLY dry.

Much appreciated!

7.5 ph is somewhat high for a soil grow, get a meter and taylor it down to around 6.1. As far as the fish water goes it to should be no more than around 6.4, the fish could also be adjusted if the water isn't perfect, your plants maybe not. They look to be green, cut back on the nitrogen some, and definitely they need more water, every 6 days seems very low, mine were going through a 1/2 gallon a day at 8 weeks they get thirsty during vege. Over watering and under watering can look similar. You don't mention your temps, RH, what type of water, etc. These help in determining causes. Hope some of what I stated helps.

Yes. Much appreciate. For some reason I was thinking 7ish PH was ideal.. but now after poking around a bit with what you said, it seems they like a little lower than neutral PH - 6.2 - 6.5 ish.

That's definitely going to make a difference - especially when my fish water is around 8. (actually just measured the fish water - it's 7 even. Still a little high.)

Thanks.