Sour Bubble - 2 weeks old DWC tubbler

I have 10 sour bubble seedlings, all but these two are happy. They are all in the same tubbler and obviously the same conditions.

These two are two of three that are about a week older than the rest. So I'm worried that what I'm seeing is just a product of being in my environment.

Thanks for any insight.

Info and pics below.

HYDROPONICS:

What STRAIN are you growing? Sour Bubble (GrindHouse Seeds)
What was the establishing technique? (Were the seed or clone?) Seed
What is the age of your plants? 2 weeks from first soak
What PHASE are the plants in? (seedling, vegetative or flower) are the plants in? Veg
What Technique are you using? DWC (40 gallon tubbler)
What substrate/medium are you using?(Hydroton, RockWool etc.) Small Rockwool cube in hydroton in a 4" netpot
What is the Nutrient temperature? 68 degree fahrenheit
What Nutrient's are you using? GH 3 part
What is the TDS/EC/PPM you are using? 360 PPM
What is the pH of the "Tank"? 5.8
Are you sure your calibration is correct on your equiptment? Yes, within 2 weeks
When was your last watering? N/A
When was your last feeding change? (ie. grow-bloom-micro-additional) 0-3-6 1ml perl gallon of CalMagPlus
What size bulb are you using? 600 watt MH
What is the distance to the canopy? 24"
What is your RH Factor? 20%
What is the canopy temperature? 74 degrees
What is the Day/Night Temp? (Include flucutaion range) 74 - 68
What is the current Air Flow? (cfm etc.) Sealed room
Is the fan blowing directly at plants? No
Is your water HARD or SOFT? Using R/O
Has plant been recently pruned, cloned off of or pinched No
Have any pest chemicals been used? If so, What and When? No
Are plant's infected with pest's No

Couple questions:
-Did you soak down your HT and RW to pH 6 before putting them in the system?
-How cold does your res get, and is it sitting on a cold floor?

I soaked the RW in 5.6 for 24 hours. They have considerable roots outside of the netpots by now as well.

The res is on a concrete floor but my temp says the water is 68-69 and the cooler is on. But that's something to check again.

How cold is too cold for the water?

--dh

That SHOULD be okay; although your temps seem to be around 5 degrees too cool overall. I like to run my res in the mid 70s though just to be safe. Maybe someone else can give a minimum desirable res temp...?
Also be aware that SourBubble is, in my experience, a picky eater- it LOOKS like it should be a pig, based on the burly structure, but really prefers a light feed. You can't give it ANY N in flower or it goes cabbagey and bitter on ya. I am running the BX3 though, so your results may vary

After looking in the sick plant sticky post with pics.. it looks to me (inexperienced) like a calcium def. What is the optimum pH for calcium uptake? Another issue to consider is normally you get a shift of pH as the eat, but with such small plants and such a large rez.. it's staying at 5.8. Is that a good pH for uptake of all the essentials? I know there is a chart somewhere but I'm having a bit of trouble finding it via search.

I'm using RO water... and 1ml per gallon of calmagplus.. is that enough?

TIA,
--dh

yep 5.8 to 6.0 should get you back where you wanna be