I did as
@Wisher2 suggested and cut one of these blocks open for investigation. Take a look!
**I picked on the smallest/sickest of the Larry OG's**
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We're obviously looking at insufficient root development for 3 1/2 weeks thus stunting the rest of the plant. Some roots have grown into the block by an inch or so, and we can clearly see limited, sporadic growth of the fluffy, hairy white roots that we want.
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However there is also significant root damage evident in the short growth, yellowing, and lack of fibrous root development.
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Possible scenarios:
[1] damping off or other pathogenic attack
[2] roots are choking and dying from overwatering
[3] other disease / root rot
A pathogenic attack might explain the leaf spotting - my research found several species of causal agents can cause this - and the pathogen would have easily circulated with my res setup and hence eventually affected other plants. Res is oxygenated but if I have an uninvited pathogen they could be stealing all the O. At first res change (day 12) the pump and hose was slimy which at the time I figured was a normal biological reaction of the nutes, but could also be proof of bacteria. Also res pH swings upwards, although I appreciate tap water may be doing this.
Overwatering is also highly likely and you might be able to tell here in this cross section of the Pargro block. I have left the blocks unwatered for 4-5 days and they NEVER dry out, not even close. I haven't watered in two days currently and they still retain ample water, and humidity is steady around the clock now at 50-55% (lower than planned but i'm trying to force drying here), temps 78F by day, couple degrees under by night.
At watering the res is down 5-7 gallons approx, so these 30-ish blocks with plants are holding on to a lot between them. This is a guess but I probably empty 1-3 gallons from the dehu tank every day.
I have no way of knowing if roots are in recovery or have been declining. Counting on the former, obviously.
I have left this block, chopped open and unwrapped, on the table to experiment just how long it takes one of these to dry out fully.
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Base of the Pargro block, looking dirty but is presumably from the dark nute solution concentrating after draining.
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As stated this was the weakest plant so i'm hoping the others that continue to grow are in better condition at the root zone, although it would be foolish to think they are not somehow feeling the pinch of the same problems. I have topped some to see how they respond and new growth is evidently good and quick.
Actions:
[1] Resist watering at all until they are sufficiently drying out
[2] Bennies will be cut from the next res and going KISS with the basic GH trio and CaMg until I can determine what is doing what in this setup
In the meantime should I flush with 1/2 strength nutes and Hydroguard? This sets back my 'drying' program but if its worth it to flush any salt buildup and/or excess of undesirable pathogen then I will do it.
Your thoughts?
And please don't say avoid using rockwool blocks in E&F, cos thats exactly how I feel at this point! I went with these after recommendations and ease of use/cleanliness, but i'm not really enjoying the learning curve in terms of correct watering. The plan was to transplant up to 7gal coco pots for flower, but I might well put some time into considering coco throughout the whole run.
