I see this a lot don't panic. This is due to root mass not being big enough to fill the pot after potting up and you think they don't need watering but they do lol, why? I hear you ask? Because the roots can't reach the rest of the pot yet to drink,I can see damage on lower leaves so I know it happened at least week ago maybe more. Definitely not fan burn though it should always be on minimum when you first pot, depends on heat. Fan burn always at the top and is stripey at the start and lots of leaves get it. I grow in bio bizz,they look like mine as I get this a lot because I try to force root growth after potting up by trickle or minimal feeding and inevitably leaf burn due to no water access which means leaves have no water and can't protect / use up the other water in the leaves etc
Bloody hell. What shark said. Lol
Casper they look fine. Don't worry. Ph should be around 6.5. ALWAYS! Stability is the key to growing weed. Don't listen to what the bag says, if your adding your own nutes you need to ph simple as that. Iv tried growing in it without ph and it does go to shit.
You shouldn't have to use ph down ever, unless you over shoot with up. First it depends on your water ph but the least Iv ever seen fresh water is 6.7 , if your not useing nutes yet just give plain un phed water , bio bizz light mix is good for a week or so with no nutes. All mix 4-6. When with nutes only start ph when it falls below 6.5