Deficiency or something else?

I recently started grow again in a brand new setup, 4x Northern Lights under a 600W HPS, however 2/4 plants are showing completely different problems. They are about 18 days old and are in a coco perlite medium, being fed GHE Dualpart Coco every 2-3 days.

The smaller one I suspect may be heat stress but I have since relocated the tent to a cooler part of the house, however the larger one I have no clue, however the lower leaves are beginning to yellow.

The other 2 plants in the tent are growing perfectly.

Read up on coco, it's not living soil. Feed every day, never let coco dry out. Ph and nute level is important.

too dry

Ok, im going to water them now, hopefully this sorts it out, thanks guys

Water everyday at ph 5.6-6.0

I see some similarity to HpLVd

I'm going to monitor them over the next few days and I'll keep you guys updated, from what I've seen on Google, HpLVd seems to cause sparse growth, will be interesting to see, what would cause this?

Never give coco plain water. Think of coco as more of a hydroponic media than a soil type media. Do you have EC/PH meters? I would start feeding those plants to runoff at 1 EC and then go up to 1.2 EC when the roots fill out the container. Feed them to 20% runoff, every day, I suspect it's growth will normalize quickly. When you feed to plenty of runoff, you are pretty much flushing your soil each time you feed and replacing old salts with fresh. 5.8 PH is good. Also, what is the distance to your light?

I dont have a EC meter, however I always PH to around 6 (5.5-6.5) and do water till runoff. My light is around 40cm away from the tops of the plants. I had the grow tent in a much hotter part (temps on average of 31°C)of the house, but I've moved it to a much cooler part (average of 27°C) so I think that was where half of my problems came from.

The heat was probably part of the problem, and the light is still quite close for plants that size. I think I used to lower my 600 watt HIDs to around 18-20 inches by the time they were flowering. I would raise them up a bit and see if they recover. I'm guessing the weird growth was from high heat and too close lights, you're lucky they didn't burn. Do you know what your relative humidity is in the room? An EC meter would still be a good investment at some point if you decide you like coco as a medium, but don't get one of the $10 ones, wait to get one until you can get a decent one.

Thanks, I'll move lift it up when the lights come back on, ive got a system controlling the RH in the tent, its currently at 60%. I'll definitely look into getting a good EC meter.

Hey Guys, just an update. This was definitely over-watering. I followed 1212ham and crimsonecho's advice to water every day and the conditions of all my plants got exponentially worse, so I posted on r/growingmarijuana and they said to aim to water every 2-3 days.

I've since let them dry out over the past 4 days and the deficiency in the lower leaves of the 1st plant and the deformities on the 2nd plant have all started to correct themselves and the plants are beginning to perk up again. I am going to start watering again now, but only as the top layer of coco begins to dry out. I also lifted the light way up and they are now gaining some height and are not so bushy, thanks Rurumo.