Rockwool Grow, Ph Problems

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Aagrows

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alright, new here for the sake of being at a complete loss with this darn plant. Not our first grow, but it is our first run with Rockwool. We were loving it up until recently.


Basics. Lemon kush plant, day 35 of flowering under LED. They are in a 4in cube on top of a 6in cube, sitting on a slab. Top fed, intake at 6.0ph and a ppm of 700-800. Now, the first two weeks or so, everything was great, no problems at all. Then lights turn on one morning and I noticed tips were burnt. We had fed one or two days prior, so I assumed nute burn. Ran plain water ph 6.0 through and got run off at 4.9 and ppm was crazy, like 2k I can’t even remember exactly now. It was all downhill from there. We have flushed it out, dropped ppm, raised ppm, flushed with peroxide solution, and to no avail. After the flush, our ppm settled and no longer is skyrocketing overnight, but the ph is still bottoming out. Within 24 hours it is usually going from 6.0 to about 5.4 on the lowest days. And it throws burnt tips even with the ppm hovering on the low side, even on days the ph sits a little higher at like 5.6/5.7. So my question now is may there be a root or bacteria problem, or is this something typical with Rockwool? Literally the only visible signs of this is the burnt tips and hairs, the plant itself still is growing great, shows absolutely no other deficient signs. It looks awesome, except for the burnt tips and the ph fluctuations. This could be totally foolish and normal for Rockwool, but I’m just at a loss right now with this plant and I feel like it is supposed to have more stability, hence the burn. I will try to attach some photos if I can figure it out. Feel free to ask anything you need to know, I’m just trying to sort this whole thing out incase something disastrous is brewing! So I beg of you, opinions please
 
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jumpincactus

jumpincactus

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Did you pretreat your rockwool???
 
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Aagrows

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Yes, both cubes and the slab were treated before they were put to use.
 
cemchris

cemchris

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Ill bring this back to say this:

You don't have to pretreat rockwool anymore if you are using Grodan. Havent for a while now. They no longer have a bunch of lime in the cubes that fuck with the PH. I havent flushed new rockwool in 3 years. Just fully soak and good 2 go. Dont have to let it sit in nute solution submerged (still a good idea for rooter cubes tho to make sure they get fully saturated since they are small and like to float sometimes) Slabs are a different story. The amount of drainage holes will mess with water retention/ph/ppm. I have only used slabs twice so cant really help you there.

PH/PPM drift in rockwool is usually from feedtimes and dry/wet cycles. Chasing runoff is the wrong way to go. The runoff is going to be different then what the PH/PPM in the cube/slab is. As they dry out the PH/PPM rises. Why shorter water times and more often is beneficial to rockwool to keep the PH/PPM in a certain range without a lot of runoff needed. Feed too much and you start to drown them. Don't feed them enough the PH rises and so does the PPM's in the cube/slab. You will end up with burning. There is a fine line with rockwool that is just dry enough and too dry between feeding or feeding cycles. That just takes seat time. Hard to do with slabs since you cant really pick them up to feel how heavy they are and how much they are drinking. Most likely you just need to tune your feed times. Def get a timer that does sec not just mins. My feed times change from week 1 to week 5 pretty much on a 7 day cycle.

If you want a shortcut you need to rent or borrow something to measure the wet/dry/ph cycles in rockwool. Now granted that expensive equipment and not really needed if you want to tweak it over the course of a grow but if you want 100% nailed down solution quickly that is it. No guess work or reading plants. But then again that shit is expensive and not needed unless you are on the commercial scale.

Also I would never flush rockwool unless its at the end of it life. If you have having to flush it you are feeding to strong or too often. With that being said I have run flower up to 1200-1300 ppm, strain specific, with no burning. Its doable if your feed times are on lock.

Also another thing you might consider is keeping your moms in rockwool. Once the plant gets adjusted to the feed times and schedule I have seen way better results and less "dead" time the first 2 weeks after transplant in veg. Honestly IMO the first 2-3 weeks in veg is when water times matter the most for rockwool plants and establishing a good root zone that isnt soggy and lazy. I have seen grows go sideways when this stage if fucked up all the way to the end of flower.

Just to kind of give you the heads up it prob took a full year to get my grows fully tuned to rockwool after switching from coco. I would say took about 2 full grows to get them on par with the coco grows. So don't get discouraged. Once you nail it tho.....I will never use anything again except rockwool. Period.

Just some of the things that might help someone new to wool and learn from my fuckups and save you time and money.
 
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