HELP!!! Day 24 12/12 from seed, yellowing leaves Skunk #1 and THC Bomb.

Hey people, hope someone can help/ reassure me. This is my first grow so am hoping that i am just being extremely paranoid about my girls.

I'm running a 400w HPS, 4" intake, 5" outtake attached to a Rhino filter. Temps are around 19c lights off and 28c lights on. Using HESI nutes and ph'd tap water. Everything seemed to be going fine up until a few days ago.

day 24

Skunk 1

I thought the patchy yellowing was magnesium deficiency and added some epsom salts to the feed days ago and also dropped the TNT back down to 4ml/ltr due to the yellow tips.......and raised the lights, thought there may be some heat stress on the top leaves....they were curling up slightly, like tacos.

Any advice would be greatly appreciated. Is this mg def? Do I keep adding the epsom salts to every feed?

Thanks

Heres the THC bomb

The really yellow leaves are new growth on one of the side branches.

They were both fed two days ago with the epsom salts, The skunk was feed again yesterday as it had dried out.....not completely but was pretty dry. Will both be getting another feed tonight. Run off was 5.8 on the Skunk last night.

They were only potted up to the 6" pots last week but I think the Skunk will need to be re potted into its final 8" pot tomorrow with the THC following in a few days. The roots on the Skunk are everywhere.

Don't worry mate - All is well..... hold back on the salts till u see an improvement so u are confident u have the issue diagnosed correctly