pH Crashes and EC Spikes in DWC - is this the issue?

Noob, but studying hard.

ISSUE: A couple days before the flip my pH started crashing from about 6 down to 4 (sometimes lower) in about 12 hours. EC/PPM would spike in same time period.

RIG: small (5 gal) DWC with top down and two air stones (air pump is outside the grow tent), Humboldt Seed Co. Magic Melon and Collie Man Kush (two of each) sharing same res, RO water and (prior to these issues) changing res about every 7-10 days. Lotus Nutrients (currently Bloom and Boost).

Day 12 of Flower as I write this. Plants look healthy overall (a little nute burn on a few tips here and there).

Right up until the flip I was running 1,100PPM (less than nute company suggestion) with pH only increasing slightly over time. About the time I noticed nute burn on the tips of only one strain the pH crash started and PPM spikes. I tried res changes and lowering the PPM, but still ended up with crashes and spikes. Roots are nice (no slime, no smell) and I'm using hydroguard (2ml per gallon), so I don't think it's root rot.

I have the chart from 420 Mag. that people keep posting, which suggests lowering EC and doing res changes until the issue stops. So far I'm down to 400 PPM and still having the same issues.

Then I saw someone quote this and wondered if this is the issue:

As plants uptake water they do not necessarily uptake nutrients at the same rate and as this occurs, the plants might be drinking lots of water but not eating much food. The result is that in a matter of hours, as the water is depleted, the concentration of the nutrients in the bucket can reach toxic levels. So it is critical to always under feed your plants in this system

Up until this started happening I was topping every day with nute water at a lower PPM to bring them down (e.g., if I wanted 800PPM and res rose to 880PPM over a day, I would add 600PPM water to lower the PPM back to about 800PPM). The quote above suggest that while the PPM was rising, some nutrients may have been consumed while others not, then when I added the nute-water top-up I was adding MORE of the nutes that were not consumed, raising those particular nutes to (maybe not toxic, but) bad levels which causes the pH to crash b/c the built-up nutes are acidic. In a sense, I've been chasing my own tail if that's right...

Is the cure as simple as topping up with plain, balanced water (no nutes)?

But maybe I'm over-thinking this one. (I also recognize I may have an issue caused by two strains in one res - if one wants a LOT of nutes and the other very little, that could be causing one to burn and the other to be deficient or at least leeching nutes back into the res.)

Many thanks for your thoughts
 

The8thChevron

Well-Known Member
This means that the plant is taking in more water than nutrients. Your feed is too hot. Drop your feed levels until the pH and EC remain static. Day 12 of flower, it should be finishing up the stretch now anyway, so it's time to cut the N and switch to bloom nutes. Do a res change. I wouldn't have your ppms over 900 but prefer 750-800 at this point (EC works on 3 different scales, so I'll use ppms).
 
This means that the plant is taking in more water than nutrients. Your feed is too hot. Drop your feed levels until the pH and EC remain static. Day 12 of flower, it should be finishing up the stretch now anyway, so it's time to cut the N and switch to bloom nutes. Do a res change. I wouldn't have your ppms over 900 but prefer 750-800 at this point (EC works on 3 different scales, so I'll use ppms).
Thanks, and that seems to make sense. I am in the process of dropping feed levels - however, I'm down to 300PPM now and pH is still crashing and PPM spiking (though not quite as much as it was at higher PPMs - so I'll try to keep walking it back, but at 300PPM now I don't have much further to go...

I think the small res is not helping stability.

It also seems like if the PPMs get too low (at whatever point) the nutes would start leaching back into the res
 

The8thChevron

Well-Known Member
Thanks, and that seems to make sense. I am in the process of dropping feed levels - however, I'm down to 300PPM now and pH is still crashing and PPM spiking (though not quite as much as it was at higher PPMs - so I'll try to keep walking it back, but at 300PPM now I don't have much further to go...

I think the small res is not helping stability.

It also seems like if the PPMs get too low (at whatever point) the nutes would start leaching back into the res
I am also growing DWC 5 gallon buckets right now. My Gorilla Glue Autos seem to really like the 750-800 range. They are about 3 weeks into flower. 300 ppms seems really low, you may have another negative affect and be all confused. How are your roots? Here's mine around day 12 of flower.20200720_003622.jpg
 
I am also growing DWC 5 gallon buckets right now. My Gorilla Glue Autos seem to really like the 750-800 range. They are about 3 weeks into flower. 300 ppms seems really low, you may have another negative affect and be all confused. How are your roots? Here's mine around day 12 of flower.View attachment 4639096
Nice!

lol...I wish I was growing each plant in a 5 gal res. I have one five gallon tote with four plants in it....yeah, I know...first go-around so I went with a pre-package system that allegedly holds 8 - but that seemed crazy so I cut it in half (4) but there's definiely a lot going on in a small space and I would not do this again.

So I've got them in a grow tent and have two net trellises up and several ties (mostly to shore them up at this point, but was for LST), but that makes it near impossible to do what you're doing here to fully expose the roots. I can get into the res through the unused net cups, and the roots look basically like yours, same color, no smell, no slime. I use 2ml hydroguard/gal when doing a res change.

Definitely switching to separate buckets next grow.
 

SnidleyBluntash

Well-Known Member
So for you a red change shouldn’t be a big deal, get an additional pail and fill it up with water and nutes and ph and let it sit for 24 hours, all the while monitoring the ppm and ph. . Then do the switch and continue monitoring. What you say about the mute uptake of various nutes and not others is true. The words ppm doesn’t say what’s in the ppm, so when it doubt, change the rez out. Those ppms of 1100 are high , what exact meter are you using? They can have different values.
Add plane water for a while

How much bubbles do you have going on in there? At least 2-4 stones? What kind of air pump?
 

[email protected]

Well-Known Member
Post a full plant shot mate. Be able to tell you the right strength from that.
Also I know what chart you're referring to and it fails to take into account that most nutes in Dwc will naturally drop oh once you flip to bloom so it doesnt count for much past veg stage.
That's why some companies call their ph down "ph veg" and their ph up is called "ph bloom".
Rises during veg but should drop during bloom.
 

cobshopgrow

Well-Known Member
This means that the plant is taking in more water than nutrients. Your feed is too hot. Drop your feed levels until the pH and EC remain static. Day 12 of flower, it should be finishing up the stretch now anyway, so it's time to cut the N and switch to bloom nutes. Do a res change. I wouldn't have your ppms over 900 but prefer 750-800 at this point (EC works on 3 different scales, so I'll use ppms).
its exactly the opposite.

PPM uses 3 scales converting EC.
" Typically, a ppm meter will take an EC reading of a solution in μS/cm2 (microsiemens) and then convert and display a reading in ppm. The most confusing part about using a parts per million meter is the fact that manufacturers of the meters use 3 different conversion factors from EC to achieve a ppm readout "

 
So for you a red change shouldn’t be a big deal, get an additional pail and fill it up with water and nutes and ph and let it sit for 24 hours, all the while monitoring the ppm and ph. . Then do the switch and continue monitoring. What you say about the mute uptake of various nutes and not others is true. The words ppm doesn’t say what’s in the ppm, so when it doubt, change the rez out. Those ppms of 1100 are high , what exact meter are you using? They can have different values.
Add plane water for a while

How much bubbles do you have going on in there? At least 2-4 stones? What kind of air pump?
Thanks. I have two sets of TDS and pH meters. Vivosun and HM Digital on the TDS and Vivosun and some other brand (no name on the stick) for the pH meters. The TDS meters were giving me two significantly different readings (like 100-200 PPM difference), but the pH meters were right about the same.

As I understand it, PPM is calculated by reading EC and then using one of three formulae (500, 640, 700) to arrive at PPM, so I thought maybe one was using a different formula than the other. So I'm running with the Vivosun TDS meter because it outputs data in EC whereas the other only does PPM.

Two air stones with Ecoplus 126GPH air pump located outside the tent.

I'll take your advice and do more frequent res changes and top up with pH'd water for a while.
 
Post a full plant shot mate. Be able to tell you the right strength from that.
Also I know what chart you're referring to and it fails to take into account that most nutes in Dwc will naturally drop oh once you flip to bloom so it doesnt count for much past veg stage.
That's why some companies call their ph down "ph veg" and their ph up is called "ph bloom".
Rises during veg but should drop during bloom.
These may be too washed out from the LED for you to diagnose properly - not sure of the protocol here, but was hesitant to use flash photography in my 4x4 tent.

What you say is compelling re: the chart and veg vs. bloom. Never heard of "ph veg" and "ph bloom" but that seems to make sense based on what I'm experiencing.

Is it your thought the falling pH is not a big deal as long as I keep playing ping-pong and balancing it regularly? I just hate to keep dumping what seem to me to be significant amounts of pH up/bloom in the res on the daily.
 

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its exactly the opposite.

PPM uses 3 scales converting EC.
" Typically, a ppm meter will take an EC reading of a solution in μS/cm2 (microsiemens) and then convert and display a reading in ppm. The most confusing part about using a parts per million meter is the fact that manufacturers of the meters use 3 different conversion factors from EC to achieve a ppm readout "

That's what I was seeing through my research. It was so frustrating using two new, calibrated TDS meters and getting wildly different PPM readings, so I switched and am using only the TDS meter that outputs data in EC.
 
Quick update:

Last night I left the EC at 0.62 and the pH at 6.2. Around noon today the EC was still at 0.62 (previously it was going WAY up), so that seemed good. However, the pH fell from 6.2 to 4.9 within that 22-hour period. I topped-off with some nute water that was higher pH (I did not add buffers) and brought the EC to 0.7 and pH to 6.0 - will see how that goes.

I figured the pH drop and EC spike were directly related. Interesting that EC did not change but pH still dropped more than a full point.
 

cobshopgrow

Well-Known Member
also having problems to read my TDS only pen, when the meter isnt so precise you never get if its 640 or 700.
have 2 meters who display EC and can be calibrated.
youre complete right, all meters measure the electrical coductivity and that can be converted to PPM.

seems there is hardly any buffer in your water, a tiny bit calcium carbonate could fix that.
your roots look really good, thats the most important otherwise such quick drops could be a rot problem.
but thats wildly guessed, no real idea why the PH drops that hard, normally in veg it rises, in flower it drops.
 

[email protected]

Well-Known Member
Plants are healthy, I'm colour blind so see just fine under blurples lol.
Nutes should be around 1.5ec for plants that size.
Calmag helps balance the ph swings. 0.2ec worth of that would be about right. Even if you've got hard water it's best to add a little just for the buffering.
 
also having problems to read my TDS only pen, when the meter isnt so precise you never get if its 640 or 700.
have 2 meters who display EC and can be calibrated.
youre complete right, all meters measure the electrical coductivity and that can be converted to PPM.

seems there is hardly any buffer in your water, a tiny bit calcium carbonate could fix that.
your roots look really good, thats the most important otherwise such quick drops could be a rot problem.
but thats wildly guessed, no real idea why the PH drops that hard, normally in veg it rises, in flower it drops.
Thanks. I'm using pH up to buffer, but I'll look into the calcium carbonate (bicarbonate?)
 
Plants are healthy, I'm colour blind so see just fine under blurples lol.
Nutes should be around 1.5ec for plants that size.
Calmag helps balance the ph swings. 0.2ec worth of that would be about right. Even if you've got hard water it's best to add a little just for the buffering.
Yeah our water is like 350-400 PPM out of the tap - which I thought was startlingly high since 500PPM is the threshold for safe consumption. Someone else told me to add tap water, which seemed counterintuitive to take out the solids and then add them back. On the other hand, my tap water is about pH 6.5 and if the additional solids help stabilize it near that mark, maybe that's worth a shot.

I feel like the small res is not helping things - larger res seems like it would be easier to keep stable. Food for thought on the next grow.

On the EC, if I go above 1.0 I get nute burn on the tips of 2 of the 4 plants, so I've been trying to dial it back to avoid that (I am at 0.6EC now, which has stabilized the EC jumps I have been seeing), but the pH keeps dropping to 4.5 or less within 12 hours every day. Maybe I just keep chasing it for another month until harvest...they seem to be doing OK other than the pH drops, which I keep correcting.
 
Google ‘cannabis ph ppm chart rising’ and there is a nice chart that says what to do in each case.
Couldn't find what you're talking about, but see below. I found this being circulated on several threads, but another commented pointed out that this is a veg chart (where pH is normally going up), and is not applicable in flower where pH would normally be going down.

Is this what you were talking about, or something else?
 

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cobshopgrow

Well-Known Member
everyones water can give a lot variables.
your start EC sounds pretty high, but there dont seem to be many carbonates in your water otherwise the PH wont be 6.5.
i never needed PH+ as my tap water offers tons of carbonates, PH 7.5.
would say youre fine with your PH+, it adds the buffer youre after.
Calcium carbonate is just one of many options, it dissolve bad in water, while you dont really need much to bring the PH up.
 

[email protected]

Well-Known Member
Hmm...I thought I could see some little fried tips there on the second pic. Plants that size shouldn't burn at 1ec, they should be able to handle 2ec without stressing.
Can't remember if it's P or K that causes the tips but its one of them.
What exactly are you feeding them?
Just checked but couldn't see it.
Using pk booster by any chance?
 
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