Yet another pH question

[RaggedyMan]

When I do a solution change in my dwc I'll set the ph to 6.5 and for a week or better the ph will gradually drop until it gets to 5.5 then I'll start adding "up".......every morning because it drops overnight so fast.
What element is keeping a new 500ppm solution at proper ph that is not in the old 500ppm solution?

 

[PK]

@Pennywise the god of dwc
i love it, i had a ph problem that it would rise like a mofo and you've got the exact oppesite issue

 

[Pennywise]

33E5D78B-F7FE-4CA1-AFF1-039601DFD516.jpeg

• Pennywise
• Jun 22, 2018

DWC Tables

 

[RaggedyMan]

I've got that chart but it doesn't answer what is keeping it regulated for a week or so but then all of a sudden it drops while the same parameters are being maintained.

 

[Pennywise]

Probably the plant pulling certain nutrients out of the solution.

 

[PK]

I've got that chart but it doesn't answer what is keeping it regulated for a week or so but then all of a sudden it drops while the same parameters are being maintained.

not sure if i understand this right. Your water level stays the same, nutrients stays the same but ph drops?
what is your res temp? ph does fluctuate in in differnet temps

 

[The Phantom]

Cation exchange is one answer. When elements that are positively charged ions (cations), such as calcium, potassium, and magnesium, are used by your plant they are replaced by positively charged hydrogen cations. Your pH will drop due to the excess hydrogen cations created by this exchange.

Had your plant started using up more cations? This could be why you your pH is going down.

The second answer is buffering capacity. The amount of buffering capacity your nutrient soup has the slower pH will fluctuate. Lime is a pH buffer for soil, for hydroponics your buffer is you pH up/down solution. The stronger your pH solution's buffering capacity, the slow pH will change.

Is your pHing solution hydroponic grade, non-expired, and properly stored per manufacturer's recommendations? If not this could be why your pH will rise rapidly.

 

[RaggedyMan]

Probably the plant pulling certain nutrients out of the solution.

EXACTLY what I'm looking for...... what are those nutrients that keep the ph up and everything healthy that first week but then disappear. (Maybe knowing this would be the holy grail of hydroponics.)
When I add nutrients, per every recipe I've ever used, it brings the ph down with my tap water (80ppm, 8.6ph). What nutrient(s) that keeps it stable for a week, is being pulled out in such quantity that it would allow such a drop later on (other than silica)?

not sure if i understand this right. Your water level stays the same, nutrients stays the same but ph drops?
what is your res temp? ph does fluctuate in in differnet temps

Water level drops, nutrient level drops or sometimes the same, ph drops ever so slowly. After a week or so ph levels plummet nightly. Res temps are controlled by a chiller

 

[Pennywise]

I always change my rez weekly to limit my mix from going wonky.

 

[RaggedyMan]

Cation exchange is one answer. When elements that are positively charged ions (cations), such as calcium, potassium, and magnesium, are used by your plant they are replaced by positively charged hydrogen cations. Your pH will drop due to the excess hydrogen cations created by this exchange.

Had your plant started using up more cations? This could be why you your pH is going down.

The second answer is buffering capacity. The amount of buffering capacity your nutrient soup has the slower pH will fluctuate. Lime is a pH buffer for soil, for hydroponics your buffer is you pH up/down solution. The stronger your pH solution's buffering capacity, the slow pH will change.

Is your pHing solution hydroponic grade, non-expired, and properly stored per manufacturer's recommendations? If not this could be why your pH will rise rapidly.

My PHing solution is hydro grade and I've resorted to buying gallon jugs (ph up) at a time. I've never had a problem with it rising, only falling during flower.

 

[RaggedyMan]

I always change my rez weekly to limit my mix from going wonky.

I'm a cheap ass and have been trying to go longer but I think weekly may be the solution. I have a 40-45 gallon capacity system and was hoping there was something simple I was missing like they're using a lot of (insert specific nutrient(s) here), all you have to do is add more and it will stay stable.
I've read a lot of ph posts and most reference the chart that you posted, which by the way is taped to my grow room door, but it doesn't answer "why".

 

[RaggedyMan]

Cation exchange is one answer. When elements that are positively charged ions (cations), such as calcium, potassium, and magnesium, are used by your plant they are replaced by positively charged hydrogen cations. Your pH will drop due to the excess hydrogen cations created by this exchange.

Had your plant started using up more cations? This could be why you your pH is going down.

The second answer is buffering capacity. The amount of buffering capacity your nutrient soup has the slower pH will fluctuate. Lime is a pH buffer for soil, for hydroponics your buffer is you pH up/down solution. The stronger your pH solution's buffering capacity, the slow pH will change.

This is probably the exact reason why but it's more complicated than I wanted to hear.

 

[Pennywise]

Different strains consume nutrients at different rates. No way to tell what they’re depleting. My guess would be a lot of calcium.

 

[RaggedyMan]

Different strains consume nutrients at different rates. No way to tell what they’re depleting. My guess would be a lot of calcium.

And I'm always growing up to 3 different strains in the quest for the perfect one for my needs.

 

[Pennywise]

That makes it even harder to run a tight ship

 

[The Phantom]

This is probably the exact reason why but it's more complicated than I wanted to hear.

I figured it may have been but I've been researching it lately because like you, after starting to flower I've noticed my pH drift now goes down vs up like it did during veg. Found out the increased potassium uptake for flowering can cause pH to drift down. Trying to add more potassium only makes matters worse because now there is more of potassium for the plant to take and replace with the hydrogen cation, further reducing the pH. The best thing to do is what Penny said, keep to weekly water changes. Also keep your pH in check, a lockout now will only complicate things.

 

[Pennywise]

Lockouts are hard to diagnose so do everything you can to avoid them.

 

[RaggedyMan]

I figured it may have been but I've been researching it lately because like you, after starting to flower I've noticed my pH drift now goes down vs up like it did during veg. Found out the increased potassium uptake for flowering can cause pH to drift down. Trying to add more potassium only makes matters worse because now there is more of potassium for the plant to take and replace with the hydrogen cation, further reducing the pH. The best thing to do is what Penny said, keep to weekly water changes. Also keep your pH in check, a lockout now will only complicate things.

This is good stuff. It doesn't solve the problem in a simple "add _______ to keep your ph stable" but it does explain why and that satisfies my curious mind. Thank you

 

[multiVortex]

I'm a cheap ass and have been trying to go longer but I think weekly may be the solution. I have a 40-45 gallon capacity system and was hoping there was something simple I was missing like they're using a lot of (insert specific nutrient(s) here), all you have to do is add more and it will stay stable.
I've read a lot of ph posts and most reference the chart that you posted, which by the way is taped to my grow room door, but it doesn't answer "why".

A pH of 8.6 seems a tick on the high end for tap? What I'm wondering is if maybe your tap water has a buffer in it or something. Even at 80ppm.

However, I think the bigger issue is water change frequency. Are you trying to stretch it for 2 weeks, instead of every week?

If so, that's going to be a big problem. The reason for a weekly water change is to prevent this from happening. After a week, the plants have pulled some of this and that from the nutrient buffet. Now as you're the chef of that buffet, you would really like to be able to just add back what was used, saving cost.

The problem here, and for most others, is that you have no idea what was consumed on the buffet and no way to find out. So you have to blindly reset the entire buffet to ensure it's all there and nothing missing.


Back to the tap thing for a second, I have that exact problem. There are buffers in my tap water that try to knock the pH back to around 7.2-7.5 or so. If I'm in veg (where pH naturally would rise over the week a bit), I absolutely have to use 100% RO water. Any tap, even as little as 10%, and the pH will jump up from 5.5 to over 6.5 within 24 hours.

In flower I will use a little bit of tap (15%-20%) mixed into the RO, and it will keep the pH from naturally falling over the week.

If weekly water changes make your wallet want to take shelter in a panic room, look into a fertilizer called MegaCrop. It's a single part, dry nutrient made by Green Leaf Nutrients. They have availability in the US, Canada, and the EU, maybe elsewhere too. For my 50gal RDWC I can get a 22lb bag for $80 shipped, and it will last me about 4 grows. That's about $20/grow for nutes. Can't beat that for hydro.

I figured it may have been but I've been researching it lately because like you, after starting to flower I've noticed my pH drift now goes down vs up like it did during veg. Found out the increased potassium uptake for flowering can cause pH to drift down. Trying to add more potassium only makes matters worse because now there is more of potassium for the plant to take and replace with the hydrogen cation, further reducing the pH. The best thing to do is what Penny said, keep to weekly water changes. Also keep your pH in check, a lockout now will only complicate things.

This is exactly what naturally happens. The pH will naturally drift down over the course of the week in flower. If in veg, it's usually the opposite. Just what plants do.

I've been trying out a little device made by Torus Hydro called the perfect pH. Had it in place for the last 6 weeks, and I have to say that so far I'm impressed. It works by countering exactly what you were talking about earlier, and is a natural ion pH balancer. It works to balance the ions released back to the solution, keeping the pH within the hydro range. It works. I'm not sure if it would work with a silica supplement or not, of if it did if it would "burn it up" more quickly. (My guess is it would work, but would burn it up quicker.)

I'm using a 35gal size one on a 20gal res, and it's working flawlessly. It took a few days for it to get in the groove, but once it did it's been solid.

You do have to soak it in a recharge solution every 2-3 months, but it seems that it will be worth the upkeep. It suggests to watch for pH drift when you get close to the window, and once it starts drifting close to or out of range then it's time to recharge. If running a device with a larger capacity than the reservoir where it's being used it may last even longer than their average. I figure I should get close to double their estimate since it's a 35gal device and only a 20gal res.

If it keeps on performing, I'll order a larger one for my rdwc, and more than likely another 35gal for my other 10gal res on my 3x3.

 

[PK]

confusing as fck but interesting , so in bloom the ph dropps while in veg rises.