AK47 plants struggling (others doing great)... nutes? light schedule? other?

In the middle of my first grow right now... about 4 weeks in. Did a 2 week veg (~15-16 hours a day) and am 2 weeks into 12/12. I have a basic ebb/flow setup, with a 4x4 tray under a 1000W HPS light.

My other strains are doing well... I have sour OG, 818-B, and a few others that are looking great. However, my AK47 and 'Grape Ape' strains.. not as much. I had 6 AK47... 1 looks good (little on the tall side and could use some 'bush' to it, but looks healthy at least), but one died this weekend the other 4 look pretty sad. Ialso had two 'Grape Ape' plants, one died a week ago and its buddy looked pretty bad, though it has shown some improvement since we started the 12/12 and new nutrients.

I'm mostly concerned about the AK47 and figure its probably a nutrient issue... thinking it might need substantially different nutrients than the Sour OG and 818B.

The nutrient mix I'm running right now contain (each titrated at about half the strength as on the box, as i think i had some nute-burn going on earlier):
Sensibloom A&B
Sensizyme
Dutch Master A&B (weaker than sensibloom b/c i didn't have much, probably 1/4 the concentration the bottle says)

Also used some 'Revive' and "Rhino Skin' to help with the sickly plants (since thats what they say they do... again a bit weaker than bottle recommends). PH has been kept in the 6-7 range at all times, temperature in mid 70s.

More details on the plants:
The 818B and Sour OG are all quite 'bushy' and range from 9-14 inches tall. Very green, no discolored leaves or anything. A closeup example of one is Pic 1, IMG 2004 below... an overall view of the whole thing is in Pic 4, IMG 2009.

The 'healthy' AK47 is 13" tall. Not very 'bushy' but clearly happier than the others. (Pic 2, IMG 2005 below)

The remaining 5 AK47 range from 6-8" tall. Also sparse, not much growth in recent weeks... almost like they're stuck in the veg stage. Pic 3, IMG 2007 below.

Your rockwool looks way too wet - I believe your problems are caused by drowning the plants.

angelsbandit said:

Your rockwool looks way too wet - I believe your problems are caused by drowning the plants.

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Really? In those pictures the rockwool is dry.. it hasn't been watered since last night (roughly 14 hours before the picture was taken). I had been following a twice daily, so the tray up to about 2/3 the way to the first/lowest 'step' on the outside... where i'd let the pump run for ~5-10 minutes and then it'll drain. Recently, once a day I've been replacing one of those watering sessions with simply dousing each plant with ~4 ounces of tap water (no nutrients) instead of flooding the tray, as I was concerned with early nute burn.

Should I be following a different schedule? Is Ak47 more sensitive to overwatering than others? Something specific with that strain must be up, as those are far worse than the other strains (and those strains are doing okay with this water schedule)

Rockwool holds water for a long time - if they were flooded as you described there is no way they would be dry in 14 hours.
I soak a 4" cube prior to putting clones in, and even after shakeing out the excess water they stay wet for close to a week.

I use net pots with hydroton in my ebb and flow systems. I place the 4" rockwool cube high enough in the net pot that the water/nute level is just below the rockwool. Once the roots grow out of the rockwool cube my cubes never touch the water again.

I grow AK47 as well and the strain I grow seems sensitive to over-nuteing, and yours seem to be over-nuted as well.

what is ur water schedule

I water for 15 minutes every 4 hours during lights on only - no water after lights out.

The roots on my clones grow thru a rockwool cube like yours in 2 or three days - then the roots really grow once they reach the water/nutes.

DrFever said:

what is ur water schedule

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Typically lights on: 8pm
Water 1: 8:10-15pm
Water 2: 2:10-15pm
Lights out: 8am

For a while those times could fluctuate about half an hour each way (it was basically whenever I got up), except for last weekend wherethe timer wasn't set up correctly and was on from 6pm-1pm the next day (long story). Other than that its been steady.