Why is pH dropping

Delps8

Well-Known Member
I've got a recent problem of the pH dropping. Most recent example is 5.9 to 5.3 in less than 18 hours.

Grow Equipment and Environment

Strain - AK-48
Number of Plants? 2
Growth Stage? Flower - week 1.6

How Long? 4 sets of nodes on 7/20/17
Indoor or Outdoor? Indoor
Grow Type - Hydro

Reservoir Size - 35 gals capacity, 28 gals to refill to 1/2" below net pot
Reservoir Temperature - 68 ±0 (Active Aqua chiller)
Medium - Started in rockwool

Hydro Setup - RDWC
Size (Wattage) of Light? How Many? 1 "600" watt LED, mfg says it draws 320 watts but KillaWatt reports 400.
Is it Air Cooled? Yes, cooled by internal fans.

Temperature of Room/Cabinet? Average high is 82±, average low is 72±.
RH - Average high about 72%, average low about 68%
PH - 5.8, has varied from 5.5 to 6.0

Pests - None known
Type and Strength of Fertilizers used? Fox Farm hydro nutes at about 60% recommended strength. Using the 420magazine.com "Wonder Chart" for analysis.
Size or Square Footage of Room? 2' x 4' x 8'

Using an EC + temp + pH monitor and really like it. Active Aqua water chiller is excellent for my needs. The RO unit feeds a 55 gallon cistern in the garage. The cistern temp is about 80 (August in Southern California) and the chiller brings the res down to 68 in < 6 hours.

Plants are growing very well. One is much taller than the other (note_ burn + the taller one is a beast) but both have lots of new growth that's a healthy green color.

Hydro unit has "top feed" function that runs 15 minutes every six hours.


Problem Statement
My grow is just getting into week 2 of flower and since flipping (or maybe a bit before that), my pH has been dropping every day. I'm not using any Down at all. It's all Up and 20+ ml at times.

Most recent example - fresh res yesterday, Ph'd to 5.9 at 1600. Checked plants this AM, and pH was 5.3. That's the biggest swing I've seen and it's never been below 5.5 before.

When I change the res, I don't sterilize it or clean it. I use a sump pump to empty the res and there's < 2 gallons remaining. No odors or visible dead things in the res.

I did a res change yesterday and filled the res with the mix for Fox Farms week 6 for hydro. Their chart calls for an EC of 1.6 - 1.8 but I'm using lower concentrations because based on conventional wisdom and I caused some nute burn. Right now the res is at 1.1/790 (0.7 factor).

The "wonder chart" (the chart the maps rising, static, falling for water, EC, and pH) indicates that I need a res change and to "lower EC if over 1.4, raise EC if lower than 1.0 so that's not much help since I'm at 1.1.
I did pull a dumbshit move and used the wrong conversion EC <== PPM factor. That caused some nute_ burn but that resolved a few days ago.

I've read here on 420 that a res that needs a large amount of Up may have root problems. The chiller keeps that res at a steady 68 and I add HydroGuard with a res change since it takes about 8 hours to get the water temp from 80 down to 68.
Roots are very light tan instead of pure white but there's no mal odor. The roots smell "fresh".

I think I've read one explanation for pH drops like this is that the plants are taking in nutes that result in cations or anions (I don't recall which one it was) being generated and causing a drop in pH. That makes it sound like a pH drop of 5.9 to 5.3 over night is acceptable. That just doesn't sound right to me.


Thoughts, advice, comments?
 
I'm no expert, but it seems your crop is removing something that is causing the ph to drop. If you have no other issues, just keep adjusting the ph to your target.
 
I see your point and if can't figure it out in the next day or two, I'll just go with the flow.

My concern is that it's unusual to have pH dropping and it's dropping pretty quickly. There are tons of posts about letting pH cycle up and down but the issue is that pH is rising and growers are adding Down to get it back in the cycle. Lots of talk about 5.5 rising to 6.x so they drop it to 5.5 again.

Even with a res change, my pH is doing the opposite of what I'm seeing other folks report. Then again, I've got one plant that's 42" and one that's 30 so who knows what's going on in the res.

I pumped out some water earlier today so I'm at EC 0.9 PPM 620 and pH of 6.0. I'll have a better idea of what's going on when I check them in the AM.
 
Sorry for the confusion – I top off with RO water that's not been pH'd so it's still up in the >6.5 range IIRC. The RO water is at 140 PPM residual. The manufacturer agrees that's too high so they're sending me a new membrane unit.

My practice during veg was to add water then add nutes if the EC has dropped. I've found that the RO water is sufficiently alkaline that it will bump pH a couple of tenths but I usually have to add Up, as well. I'd like to have it sit at 5.8 but it drops so quickly that I've taken it to 6.0 a few times.

I've been dropping the EC since it went into flower. Going back at least a couple of weeks, I was using the wrong conversion scale on the monitor so I was 40% over strength. That resulted in nute burn but not catastrophic - some leaves were seriously damaged but most only had tan or light brown spots that were a few millimeters across.

After the res change yesterday, I've continued to pump out nute water and replace with RO to get away from nute burn and to get it low enough that I have to add nutes. That's the "let the plants tell you what level of nutes they need" approach.

At 6 PM tonight I added ½ gallon of water with EC at 0.9 (620 PPM) and pH at 6.0. Just went to the garage to let in some cooler air and sure as shinola it's 620 at 5.6.
 
As I say, I'm no expert. In fact I'm a soil grower. We all certainly want to understand what's going on with our chemistry, soil or hydro. Perhap you should try a different part of 420. Some plausible speculation might help you at this point.
 
(Scratches head) Take a gallon of water, prepare it exactly as you would before you add it to your res. Monitor the ph of this gallon. Does it drift, low, high?

If it does change, it would seem you have some interaction between nutes, and h20 that cause a shift in PH. If it stays steady, that suggests that adding the crop into the chemistry introduces another variable, which is the reason for the PH drift.

Sorry, buts thats all I can think of. There are some greater minds than mine on here. You need one of them...

I use RO water also. It's notorious for having no PH buffering qualities, but I bet you know that...

Could this be a measuring issue with the PH meter?
 
I work with RO water at my job and use it for my grow. RO water is stripped of pretty much everything in it. As a matter of fact it's not encouraged to drink RO water if you're very thirsty. It could pull minerals from the body rather than assist. I'd say your plants are pulling so much from the nutes that what regular water naturally supplies your lacking.
 
OH:


"As I say, I'm no expert. In fact I'm a soil grower. We all certainly want to understand what's going on with our chemistry, soil or hydro. Perhap you should try a different part of 420. Some plausible speculation might help you at this point."
There are so many nooks and crannies on 420 that I wasn't sure where to post. This seemed like a good spot but maybe I'll forage through the menus and see if there's a more suitable place.


"(Scratches head) Take a gallon of water, prepare it exactly as you would before you add it to your res. Monitor the ph of this gallon. Does it drift, low, high…adding the crop into the chemistry introduces another variable, which is the reason for the PH drift."
As in "troubleshooting via executing a logical sequence of steps"?
Agreed. That's a good next step to take. There's only so many big chunks - water, nutes, plants, temp, RH, and the res itself. Sure, there are lot of pieces to each of those but, off the top of my head, those are the big chunks.
That's a slow process but I'm beginning to run out of ideas.


"I use RO water also. It's notorious for having no PH buffering qualities, but I bet you know that..."
I know that but only as a fact not by how that impacts things. The latter is experience which is something I'm getting, one painful event at a time!


"Could this be a measuring issue with the PH meter?"
Don't think so. It's a new unit and it is reporting a range of values. It is worth double checking, though.

Thank you!
 
"The latter is experience which is something I'm getting, one painful event at a time!" and that's the way it's done.

Re meter. I calibrate mine before each grow, and treat it very gently.

I actually use a combination of ph adjusted tap water (with a high mineral content), and ph adjusted ro water with calmag+. All the nutes (at low concentrations) are mixed with the ro water to avoid salts buildup.

Re trouble shooting: Yes... control variables and analyze the results.
 
Have you tried mixing calmag in your ro water before adding it? Im no hydro grower but I know when I use distilled water or ro water the pH changes drastically with one or two drops of pH down and the pHed mix always drops by the next day. I was told on another site to mix my Ro water half and half with tap water that has had a chance to dechlorinate. Ive been doing this for a few years" when I use distilled" and it works to help keep the pH from spiking. Distilled or Ro water has no minerals or foundation for the pH solution to hold onto, adding calmag to the water before adding it to your res may help condition the water to be pHed. Just a thought...
 
OH

"My residual is 11 ppm... down from 158 ppm before tx..."

Hah - now you're bragging! :)

It's a new RO unit and it fills a water barrel in my garage. At times the PPM for the water from the barrel is 140, other times it's 70-80. The manufacturer sent me a new membrane and I'll install it over the weekend, after this bloody heat wave passes.
 
Luweedgi:

"Distilled or Ro water has no minerals or foundation for the pH solution to hold onto, adding calmag to the water before adding it to your res may help condition the water to be pHed. Just a thought..."

That's a concern, no question. And there's also the fact that if my RO membrane is leaving some of the TDS in the water.

One of the problems that I had with nute burn was also a mag deficiency. Fortunately, adding CalMag seems to have cleared that up.
 
As Old Hippy said:

"The latter is experience which is something I'm getting, one painful event at a time!" and that's the way it's done."

"Those aren't scars — those are experience!"



I called tech support at Fox Farms. The salient points:


1 - pH will drop when there's more nutes than the plants are taking up (if I pump out more water, I'm going to grow webbed feet - this can wait a few days)
2 - "I'm going to be worried if I drop a whole point in a day" - my ½ point swings are OK
3 - pH will change as the plant changes what nutes it needs and as conditions change
4 - General Hydro pH Down is not as strong as Down from other manufacturers so try switching brands. The person I spoke with said that they can't recommend a particular brand.

Called Botanicare tech support because they sell Down. I told him that I was using a lot of Down but didn't state the manufacturer. Perhaps it was a WAG, but he asked if it was GH saying that GH isn't as strong as their Down. Also, he said that he's used FoxFarm and has experienced the need to add Down vs when he switched to Botanicare when he started using Up. He said that nutes from different manufacturers behave differently so it wasn't unusual to see that I was adding Down or that my res was dropping like that.

Both tech support personnel said that the fact that pH is dropping indicates that the plants are taking up nutes and that a drop like I'm seeing is not an unusual situation. The key point is that the plants are growing and new growth is healthy and, second, seeing that tech support personnel from both companies said that GH's version of down is not that strong, I've got a quart of Down from Botanicare on the way.

Maybe the lesson learned here is that the only thing that's "wrong" is that it's not good to have pH dropping (or rising) "a lot" and to a grower that means more than a few tenths of a point. In contrast, for the folks who work in the nute companies, there's nothing to worry about until you're looking at a change of a full point.

That bit of info goes in the knowledgebase.

Other point, about the RO - I have the new membrane and will set it up over the weekend. That should drop my PPM to 0± and, I hope, will allow more nutes in the water than whatever chemicals are floating around in it now.
 
I have always suspected that the nutrients companies suggest we use more than we need. I rarely get to 1/2 the concentrations they recommend. Noted that on my first grow.

What you reported make sense, and is in line with my experience. You may indeed be trying to fix something that is not broken. We all have been there! :)

As for that new RO membrane bringing your ppm down to +- 0 ppm, good luck with that. (95% reduction is great--- 90% is good, and 75% commonly means you need a new membrane.

I use Advanced Nutrients PH down. Great stuff, you sure don't want to get any on you though...

Best wishes, from a real Hippy...
 
I have always suspected that the nutrients companies suggest we use more than we need. I rarely get to 1/2 the concentrations they recommend. Noted that on my first grow.
That's what I've read in a lot of places and that was the case throughout veg. I was at about 60 to 70% of recommended and it went fine. After screwing up the conversion factor, though, I was way over the recommended amount but caught it pretty early. Some of the leaves had brown spots but I'd guess about half a dozen were burned and yellow - very dead.
At this point I'm at 58% and am no rush to change anything.

What you reported make sense, and is in line with my experience. You may indeed be trying to fix something that is not broken. We all have been there! :)
Heh, I appreciate that. In retrospect, I pulled the trigger on this too early. It's good to document it so that others can search on it and read it but it looks like this really was a tempest in a teapot.

As for that new RO membrane bringing your ppm down to +- 0 ppm, good luck with that. (95% reduction is great--- 90% is good, and 75% commonly means you need a new membrane.
Good numbers to know. I was expecting to hit those low numbers so I called the manufacturer and they FedEx'd a replacement. I hope to get those numbers with the new membrane but that's a variable I don't want to add in right now. Plus, I do have to get some work done!

I use Advanced Nutrients PH down. Great stuff, you sure don't want to get any on you though...
Oh, thanks for the warning. AN also has a line of nutes that automagically keeps pH stable. I pondered that vs Fox and decided on Fox. Could definitely change that in the future though.

Best wishes, from a real Hippy...
Thank you!
 
Heh folks, don't mean to beat a dead horse but I'm lost here.
I'm in week 4 of flower and I'm getting "plummeting pH".
I've culled what might have been a "damaged" plant, changed the res doing "everything right by the book" but my pH is dropping by the hour.
The plant looks really good - solid green color, growing like fury (more than doubled height since flower), and no indication of nute deficiency.

Damaged Plant
I ended up with two AK-48's, Norah and Nancy, going into flowering stage. When I culled Nancy, she was about 28" vs Norah at 55". Nancy's roots were OK, she had a little bit of a magnesium deficiency but she had only one stem that was "growing tall and flowering". Seeing that her yield would be close to zero and also that Norah is a beast, I tossed her out yesterday before I did a res change. I wanted to remove all variables to try to resolve the pH insanity.

By the Book
Res change yesterday. RO water, pre-chilled to 70. Cleaned the res walls and pumped out the "silt" that was on the bottom. New water going in (no nutes) was 60 PPM (0.7 scale) which is an EC of real close to 0.
Checked PPM and pH readout of recently calibrated Bluely monitor against pens. Both were within tolerances/margin of error.
EC is now 0.8 (540 PPM on 0.7 scale) and it stable.

My setup uses an LED and RO water so I "should" use CalMag. Seeing that I've had big pH swings in the past and that Fox Farms tech support told me that I didn't need CM with their nutes, I did not add CalMag. Water chiller keeps the water at 68º. Light is as high as it can go so I've got just over 12" between the tops of the plant and the light. I've had to supercrop in flower. Some of the leaves at the top are curly down but they are sold green - no sign of burn.

Tent temps have been very stable. I installed a portable AC unit to get through the very high temps a few weeks back so the temp range has been 73 - 80 for a couple of months. RH is higher than I want, getting into the 70's at night but down to 60's during the day.

Not By the Book
#1 - I dicked up at some time in the last few days and hit the "random" button on my light timer. I discovered this when I checked the tent after 8 PM and the lights were on. My suspicion is that was the first night where that occurred but I can't be sure. I'm now back at 12/12, 0800 to 2000.

#2 - Nute manufacturers warn that you should put nutes right into the res. Since I have had no idea how much I'll need, I mix one batch of nutes, with water, in a 1 gallon water jug and then add that to the res. I'm not mixing "just the nutes", I'm mixing them in about ½ gallon of water and using the jug as my nute store. When I add them to a fresh res, that batch is just a few minutes old.
When I add small amounts of nutes, I'm careful to shake the big bottle, pour into a plastic measuring cup and dump the entire content into the res quickly enough that the solids from the measuring cup get into the res.

When I say plummeting pH, I went from 5.7 at 2230 last night to 4.8 at 0800 today.
Here are some readings from this morning.
Time//pH
1013//5.9
1020//5.8
1035//5.8
1044//5.8
1110//5.7
1143//5.6
1217//5.5

I realize that pH will change but it makes no sense to me that I'd drop from 5.7 (a bit low) to an acid bath of 4.8 in about 12 hours.

The only options I can think of are s
hould I just shut up about this and glug in the Up ("Better living through modern chemistry!") or raise//lower the EC, gradually, until I hit a level where the roller coaster stops.

Anyone have any other ideas about this?

Many thanks.
 
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