Rockwool Croutons Ph Rise Issue.

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blitzman734

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So i've been growing a couple of plant's capn style (not important you'll see why) but i've been essentially growing in rockwool mini cubes and have had a hell of a time keeping my ph some become too alkaline daily. I'll water in at 5.7-5.8 and my res will be 6.1-6.2 after one watering. This stumped me for awhile so I went back to basics and ran a best of a test to eliminate variables.

I presoaked a 6inch net pot worth of croutons in 5.5 water as called for by grodan for 2 hours to make sure all the lime from the manufacturing process was out. I did not place any plant in these cubes but gave it a 5.8 watering the next morning and checked the runoff and noticed immediately that it was 6.0. I gave it a couple of hours to dry and ran more 5.8 through and still 6.0 coming out.

Grodan claims without the lime these cubes should be pH neutral but they seem to me to be leeching out the acidity immediately in some strange way. I understand this drift is ok plants like a range of pH to absorb all nutrients blah blah my issue is that I want to feed multiple times a day but can't because recirculating this water continues to rise the pH so res change happens and input water is 5.8 after I run a cycle the res is now 6 and with one more watering its now 6.1-6.2 and with another 6.3. I could add pH down and I have for a lot of this run on an almost daily basis to maintain and i've since switch to just drain to waste to keep her healthy and take the hit on the nutrient costs but seems crazy to me why this is happening with a medium thats supposed to be pH neutral.

Have others experienced this? I'm using RO water, there is no algae in my res or in my test environment without a plan I can simply pour 5.8 water or 5.8 nutrients through these cubes and immediately see some acidity removed.

Any advice is appreciated as I would love to continue use of the medium. I had amazing root growth and it was very clean and easy other than this pH issue.
 
Smokey503ski

Smokey503ski

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I found that if you squeeze the rockwool you can get more of the nasties it.
They will reform there shape when dried.
 
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blitzman734

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Interesting, i never heard the full explanation as to why not but i've been told multiple times by a variety of people never to squeeze rockwool as it compromises its man made structure which gives it the water / air retention quality that makes it such a good medium to grow in. I may try with my test batch though and ill report back on if it helped.

EDIT: I've found multiple articles online of people complaining of this exact problem and although i've seen mention of squeezing being bad for the air pockets i'm going to soak for longer again in some 5.5 maybe even 5.2 or 5.3 and give a light/medium squeeze.
 
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baba G

baba G

bean sprouts are tasty
5,290
313
Dont squeeze the rockwool! It smooshes the air pockets and they dont reform...just soak overnight and see if that helps or with a lower ph soak but longer soak time should help.
 
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blitzman734

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I didnt lol. I actually took a trip to my grow shop and talked to a guy who grew for a couple years commercially with the mini cubes. He confirmed what i was seeing and claimed grodan was full of shit about being ph neutral. The lime from the manufacturing process cannot be completely removed and the presoak brings the level of alkalinity down he never saw anyone be able to be able to recirculate for this exact reason.

My next run with be in coco i think. In the 7 gal smart pots im having to push two gallons a day to kept them moist. They are healthy happy monsters but the waste is just too high to want to continue with.
 
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blitzman734

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So just an update to this. I converted to drain to waste getting at least 15% runoff as called for by grodan. Apparently its engineered specifically for this level of runoff so regardless of how dry it may seem on top the root zone still has the proper amount of moisture and continues to feed the plant. I still water daily from a res just without recirculation. I may manually recirculate once on this next run at least one time through.

Side note. I also stopped feeding florablend with this batch as I believe the compost tea aspect is breaking down due to aeration, etc and is causing some brown looking (no smell) algae. I will monitor but likely been hapenning since beginning and pearly white roots. Just applying recharge twice a week.
 
WhoopDeeDoo

WhoopDeeDoo

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Rockwool Croutons for the Win!

I just use 1.5 gallon mesh bottom pots and water really well the first couple of times with significant amount of runoff to prevent PH swing.

After a few waterings everything becomes very stable throughout the rest of the grow!


Sb25
 
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blitzman734

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Hey Guys,
I think I was misunderstood a bit. The pH swing was happening in the res not in the media or root zone. That has always been fine. What I'm curious on is when you take a 5.9 adjusted feed and pour through even if you flood for a bit it still comes out 6.1 or higher. That obviously was an issue I was having to address constantly when I went to feed my plants as the runoff that was recollected after a couple days was 6.3-6.4 in a hurry. I'm not sure if you guys are recirculating or not.

Not sure if you've heard of him but I was following a methodology of growing by a person named capn. http://dudegrows.com/lets-captain-style-baby-part-1/ for reference. He recirculates but feeds for 15 minute cycles taking advantage of the engineered croutons ability to not be overwatered ensure pH and flushing out every feed essentially. Although now I can see why this is unnecessary I was stunned at first at how he would be able to do this for more then two days without constantly adding pH down because of the acidity being leeched a bit every run through the croutons.

I will say though aside from that my plants are super happy. I've got two trees at the moment I vegged for two months a piece and they are monstttters in the croutons. Monster may be a poor term to describe them. I'll say that each plant could fill a 4x4 without a trellis lol. Although his watering method is suspect capn typically pulls 16-20 oz per plant with these croutons and extended veg period.
 
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blitzman734

10
3
Rockwool Croutons for the Win!
I just use 1.5 gallon mesh bottom pots and water really well the first couple of times with significant amount of runoff to prevent PH swing.
After a few waterings everything becomes very stable throughout the rest of the grow!
View attachment 599854

WhoopDeeDoo,
Thanks for responding man, first off holy crap you have a nice grow room. I am very impressed. I shot you a pm to chat about some details of it.
 
Dr.Pepper

Dr.Pepper

233
43
i think you may benefit from using a Base Nutrient formula like Canna Aqua A&B or H&G Aqua Flakes A&B that is designed for recirculating system with pH buffers that will help stabilize your res pH.

I have read alot about how these two Base Nutes make a big difference in recirculating systems instead of old standard hydro formulas out there.
 
mojavegreen

mojavegreen

707
243
Meh, GH maxi bloom and maxi gro is pretty damn stable.
 

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