Rockwool PH

[lysol]

I am testing rockwool PH with runoff + a syringe, since I killed my first batch of beans I want to get it right on this second $80 batch of beans. Yes I have free seeds I could use but I am stubborn and this shouldnt be hard to germinate.

Anyways the runoff comes out at 6.5+ ( just under 7 ), watering with 5.4 tap. If I soak the cube or water it enough ( ounces of water ) I get the runoff down to 5.7 range.

Now heres a neat trick for drying out the cube after soaking it. sit it ontop of a towel. Wait 60 seconds, half the water will be gone, after 3 minutes the cube will almost be dry, gravity causes the towel to wick all the water down.

SO anyways after I dry the cube I water again and runoff comes back out at 6.4 - 6.5.

Now I did some research and read some hydro books on google books and I am under the impression the 5.6-6.4 PH is only to offset the high PH of the medium, am I under the impression your medium should be 7.0 nuetral? Because these damn cubes seem to want to stay right there.

 

[Sportster]

..are you soaking the cubes in the 1st place??

something you don't want to do when using RW anything!!!

 

[dongle69]

Why are you drying out the cube?
This info from Grodan may help:

It is a common misunderstanding that Grodan is alkaline and that one has to continuously adjust the pH, when in fact Stonewool is pH neutral.

The confusion stems from the fact that Grodan has some residual lime from production. Follow this simple procedure to remove this un-buffered lime. Begin by saturating the stonewool in pH 5.5 water ½ hour before use. There will be a rise in pH of about 1.0 from the residual lime dissolving. The final step involves flushing the “dissolved Lime” from the stonewool with your nutrient solution just prior to planting or sowing. From this point onwards, the pH neutral Grodan Stonewool will not contribute to any changes in the pH of the solution.

You can soak the cubes on your table. You don't need to cycle, as long as the cubes are soaked initially. However, you do need to add the final step of watering from the top in order to flush out the lime residue. You should also get rid of the drained water, as it contains the lime residue.

There is lots of good info at Grodan's help site:
http://www.hydroponics101.com/

 

[lysol]

The package said no presoaking is needed but yes I soaked it for about a half hour. I water from the top and have been sucking up the runoff and adding it back to rez, the rez PH seems to be stable but maybe this lime is getting in there. Sportster what do you mean? I'm a little concerned because the beans are in there and I dont want them to overwater thats why I let them dry out. Also so I can top water more soon, to flush out whatever was in there ( which I now have learned is lime !)

 

[lysol]

Ok so I let a cube sit for an hour + ( threw it in the rez way before I made this thread. )

The ph of the water it was sitting in was 5.5

Took the cube out, dumped the water and cleaned bucket, filled back up with php 5.6 water

slowly dumped 1.5 gallons of water a cup at a time thru the cube, making sure it was evenly flushed, filled up bucket again and repeated with another 1.5g flush ( on a 1" cube ). Watered with 60ml of 5.5 water and measured runoff at 5.8.... ok not so bad.

Speed dried the cube on a towel and did the runoff test to get 6.4

If drying the cube on a towel shifts the PH almost 1PH in 3 minutes the cube is obviously not safe for my seedlings once they start needing nutes?

One of the beans is really liking the fast water cycles and has just popped :-D I wonder if this downward wicking action could be replicated in an ebb and flow setup? No idea how youd keep the wicking medium dry tho.

So just to confirm the PH of my runoff should stay at 5.6 - 6.4 correct? I have measured runoff at 7+ with the exact procedures I outlined... I will continue flushing and soaking this test cube for up to 24hrs. I bet grodan was just like you know what guys, lets say no presoaking needed, sure peoples plants will die but all that means is theyll need to reeup our cubes faster

 

[Sportster]

What I ment was.....when I use to use RW cubes to start seeds and root clones, I would soak them up with RO water, ph adjusted then I would "shake" them real good twice, careful not to squeeze them to hard, and I'd do this is an area like the shower, or outside, you do NOT want to squeeze out the excess of course...

By shaking the cubes out a bit allows pockets of air to be trapped in the cube, and thus not allowing you to saturate your seed or cuttings, AND!!! when the roots appear, they shoot for those pockets of air which they need to sustain life and grow...

I was more concerned for your lose of expensive seeds rather than the pH levels of RW's run off....personally, I just pH adjust RO water to 5.9 if I think about it, otherwise I just use the RO water to root and start seeds!!!

 

[lysol]

Ok cool, K+ on the tips everyone so far. I am most concerned about my seeds but I also cant stop learning, the chemistry, science it all fascinates me... I read about people not soaking their cubes and my experiment shows they are running at 6.5+

So.......... what I read then must be true, the _reason_ we run 5.5 PH is to offset the cube, if only it werent for the cognitive dissonosance with grodan saying the cube will not affect the PH, doesnt make sense. Does anyone know why we run 5.5PH? I know that is the range best for nutes absorption but why is it different in soil? The medium must be alkaline despite grodan's marketing prose?

 

[pontiac]

Rockwool naturally contains lime so it'll cause the pH to rise up gradually (even after multiple readjustments) for a while (a few days to a few weeks) until the lime dissolves away.

 

[lysol]

Ok thanks, and is there any chance the lime could outlive the seedling, that is... when the seedling develops leafs at 4 days my runoff PH better be stable at 5.8 or else theyre going to die, correct?

That same cube has been sitting wet and is now back up to 7.0, the thing is, this was a cube that was soaked and watered for days ( the first time I soaked it was not today ) the thing just seems to be stuck exactly at neutral, i dont know.... I'm probably just being a noob though

 

[Sportster]

Have ya tried Rapid Rooters?? once I discovered them, I never used RW again!!!


'jes a thought!!!

 

[pontiac]

Rockwool manufacturers change their manufacturer techniques and source of stone all the time so it's difficult to know how much lime a certain batch of rockwool contains and long it'll take for it to stabilize. For example, in current my grow, I'm 2.5 weeks in but I'm still experiencing a creeping pH problem (but it's negligible compared to the first week).

Nevertheless, I doubt your seedlings are going to die from short term pH shifts, just keep a close eye on the pH keep it between 5-6 if you can; optimally 5.5. Don't be too obsessive and readjust it every chance you get; just do it say, at every feeding.

 

[lysol]

Havent tried rapi rooters, maybe someday. Maybe if there was a grow store within a billion miles from me heh.

In your thread your rockwool seedlings look a little bad ( no offense ), I was reading your thread the other day you said it was due to himidity, on second thought do you think the lime in the rockwool could have contributed to the deteriorating seedlings?

I need to figure out the proper sequence, please help:
1: lift cube, if light dont water
2: add 10-20ml of water to 1" starter cube, or water until runoff? which one?
3: suck up runoff with syringe and put it into shot glass, measure PH
4: if runoff is high, keep repeating steps 2-4
5: done

And you are to feed at every watering? Or only the first 10-20ml, and then plain water to get runoff? Would you say bringing 150ppm tap water to 200pm would be sufficient for seedlings? How long can they live off plain tap.

On my last batch I got curled over leafs with yellowing tips, definitely N lockout and watering issues, I am concerned now PH also had a play into it because right before they died the leafs exhibited twisting, stem thinning as well. They were hit with .5EC and 1EC nutes though ( 2 different tests )


Cliff notes: Do you water until runoff and what PH do you aim to keep your runoff at. Do you PH your water lower then 5.5 to help keep the PH low ( despite it "damaging rockwool"?, e.g. dustmasters conditioner is ph4 ), do I feed at every watering and how low of an EC does a seedling need. I thought they needed 800ppm but turns out thats tomatoes.

 

[Sportster]

Havent tried rapi rooters, maybe someday. Maybe if there was a grow store within a billion miles from me heh

I am sure they can be found online....I am glad you changed what you said...LOL!!!

I dont feed until the seedlings or clones become more of a plant, surely not everyday....and your "N" lock out??..how do you know you didn't fry them with too much "N"??...a lock out prevents the plant from uptaking nutes, you described what sounds like too ~hot~ of a mix for the babys....

I understand your a learning magnet, BUT.....I see no reason for all this science and questions, its really not that difficult to achive, but I've seen folks over LOVE their plants to death, time and time again over the years!!!

 

[lysol]

Yeah I ordered online but I want to keep reups to a minimum for max stealth. Yeah I figured since my nutes were so hot it was locking out N due to some other nute being in abundance. I definitely first experienced N deficiency ( but the nutes were there, so the plant was not eating ). Probably too strong of ferts and overwatering, yeah it shouldnt be this hard I'm confident my 2nd batch will do better, we'll see... This isnt my first grow but its my first soilless. I tried a bubble cloner in the past and killed my cuttings so Im off to a great start

 

[Sportster]

Is cool on the 1st time thing, Ive been at this for over 30 years, and indoor hydro for the last 10 and I am STILL LEARNING!! its a never ending process, and like computers.....you better stay a-BREAST of whats new an whatnot!!!

bubble cloners/ghetto cloners/NFT mist cloners all take some know how I feel....I've tried them, and of course went back to what I know works best for me... Rapid Rooters!!!

I understand your privacy thing, I happen to live in a state where I am a legal grower...so I tend to forget these kinda things at times!!!

 

[pontiac]

Those weren't seedlings, they were cuttings. For cuttings, such stressing is normal (in other words, not related to the rockwool) because they didn't have a root system for a while. After rooting, the cuttings became clones and grew like normal plants from there, but that's another story. In your case you have seedlings which root immediately so you shouldn't expect the same stresses as with the cuttings.

Now with seedlings, I usually get a 100% success rate (by that I mean no deaths or even sickness) after germination; there's nothing really complicated about it. Here's how I usually prep them in rockwool for transplant to a hydro system or potted soil:

Soak rockwool plugs in warm pH 5.5 water for 24-36 hours. In the mean time soak seedlings for germination.

Thoroughly rinse rockwool plugs.

Get a gallon of distilled water (which is usually <15ppm @ 0.5) from the supermarket and mix in veg nutes to a weak solution of 200-300 ppm @ 0.5.

Adjust the pH of the solution to 5.0 (it's a little more acidic to counterattack the remaining lime in the rockwool)

Place sprouted seedlings in rockwool plugs, taproot down.

Soak all plugs with the solution and keep plugs in a heated humidome.

Test the pH of a plug by firmly pressing a pH test strip against it. If the test strip reads too alkaline, re-rinse all the plugs with the solution, this should bring the pH of the plugs back down to optimum levels.

After roots appear out of the plugs, transplant them to a hydro system or pot.

Good luck!

 

[lysol]

Those weren't seedlings, they were cuttings. For cuttings, such stressing is normal (in other words, not related to the rockwool) because they didn't have a root system for a while. After rooting, the cuttings became clones and grew like normal plants from there, but that's another story. In your case you have seedlings which root immediately so you shouldn't expect the same stresses as with the cuttings.

Yeah I guess the light spectrum in your pic made it look more like brown leaves then the N def. you experience as the clone transfers stored N from the leafs to build it's root system. Anyways this time if they start looking bad I will react much sooner and much less drastically.

 

[lysol]

I have had to flush 2x a day and then re-feed to keep PH acceptable, but theyre loving me for it!

I bring the PH down really low like 5.6 or 5.7 and its back to 6.5 later in the day


So my question now is if I plant in rockwool in my DWC bucket, the water in the cube will most likely rebuffer itself to ph7 from the lime in the cube... Will the plant be able to feed from it's roots in the grow rocks? Or does it work more like an average of the PH in the cube and the res? I suppose if I planted it I should just pour rez water thru the cube a few times a day to keep the PH stable? Or should I let my plants veg in 1" cubes for 2 weeks until this damn lime is dissolved? I have like 10 roots thru the bottom half an inch long already

 

[dongle69]

I am curious what brand of rockwool are you using?
It sounds like you have some industrial grade stuff.

 

[lysol]

Grodan mini cubes, I put 2 in their buckets last night and 1 this morning they look like their going strong so far. I am just wondering if I should worry that the cubes are raising in PH I am 99% positive they are I am just wondering will the plants just get their nutes from the hydroton or does the PH like kinda average out?