PH dropping in stand alone reservoir - But why?

[gr0w]

Hey guys,

My last grow all I did was pH down, hardly ever had to pH up.
This grow is the complete opposite...??

I am using a stand alone reservoir that feeds the plants on a timer.

Info on my setup:
-System is Drain to Waste
-I am using Reverse Osmosis water
-I am using REMO CalMag, and general hydroponics trio nutrients. (Micro, grow, bloom)
-Using HydroGuard every res change
-Room temp is 70*F (tent is 78*F)
-Reservoir is outside of the tent
-have two large air stones in the reservoir

I am just wondering why, and what would cause pH to drop from 5.8 after res change to 5.2 a day later.
-I get why they would drop if the plants were directly introduced with the nutrients solution, but if it’s just sitting in a reservoir, what would cause it to act like this?

I recalibrated both my pH pens and they Re reading the same, so that’s not a problem.

System is a drain to waste and the waste is collected all into one container for easy removal.

Here are some pics of the system to visualize what I am talking about:
*note: lid is always kept on the reservoir*

 

[Scientific]

If I'm understanding your setup correctly, what you have that is relevant for discussion is basically a bucket of fertilized water with a couple of air stones.

Are you adjusting the pH of the solution after you add the Ca/Mg and FloraSeries? (By the way, you know that you add the Ca/Mg first, right? That's what GH recommends anyway. I think that's because the Ca/Mg stock is at an alkaline pH and needs to go into solution first. If you put it in an acidic solution the Ca and Mg crash out of solution. I think I have that right...)

If you are adjusting the pH downard, given how simple the system is, I'm going to guess that the acid in the pH Down is fighting with the buffering in the FloraSeries nutes and only winning after the solution has had a chance to sit for a while. I think that's a pretty good guess since there isn't much else going on, and buffers by their very nature resist changes in pH so will have a time delay if you add acid--that's what makes them buffers. (One simple example would be adding acid to a container with a piece of chalk in it. It takes some time for the acid to dissolve the chalk.)

Personally, when I mix up a batch of FloraSeries nutes, I don't adjust the pH and just leave it at the 6.x pH it comes out to naturally.

The whole point of having a complex buffering system and chelation and everything is that the nutrients are available over a broad range of pHs so you don't have to worry about that.

Here's a great article: Advanced Nutrient Management — General Hydroponics

 

[gr0w]

Yes, just a reservoir that is on a timer to send nutrients to plants on a timer, then it drain to wastes into a different container to collect the run off.

Yes, always do CalMag First then trio, then HydroGuard.

My last grow I was adjusting pH down as normal with the pH drift.
But this grow I have been adding pH UP every reservoir change and it tends to drop from 6.0 to 5.4 once a day.

Just curious as to why I'd be adding pH up this grow if it's the same system used last grow and I was adding pH down.

Could water temp/ room temp be a factor?
Or
maybe too much CO2 introduced into the nutrients solution?

I don't mind having to add ph up; just trying to wrap my head around why it's dropping so rapidly.

Thanks fir the article.
Good read, it's hard to find info I am after cause most systems have the plant introduced right into the nutrients mix, but not on mine.

 

[Scientific]

pH doesn't vary very much within the range of room temperatures, so that's out.
Unless you're actually bubbling CO2 into the mix, I doubt that's it.
And this is just the nutes that have not been exposed to plants and everything else is the same?
I don't get it unless maybe you're water has changed?
The question here seems to be, "What changed between last time and this time?"

 

[gr0w]

pH doesn't vary very much within the range of room temperatures, so that's out.
Unless you're actually bubbling CO2 into the mix, I doubt that's it.
And this is just the nutes that have not been exposed to plants and everything else is the same?
I don't get it unless maybe you're water has changed?
The question here seems to be, "What changed between last time and this time?"

Yeah, nutrients that haven't been exposed to the plants. Just sitting in the container waiting.

Really Nothing has changed, still the same exact system, same nebulas GH grow chart feeding schedule.
Maybe I'm not adding enough CalMag, or too little?

Or maybe my RO water filters are coming to the end of their life and not filtering out enough, I'll have to check, but the last time I did (2 weeks ago) it was @ 7PPM

Can't seem to wrap my head around this one.
Just wanna figure it out so I don't have to keep adding pH up and messing with the nutrients solution.

Doing a reservoir change tomorrow for 2nd week of Early Bloom, so might take some readings after everything I do and document it and try and figure this thing out.

Thanks for your help Scientific

 

[Scientific]

Thanks for your help Scientific

I wish I had been of some help. Weird problem. Oh well, not life-threatening.

 

[DoItToIt96]

I have been having the same problem, but I think I have solved it for myself. I have about a gallon of tap water at this point, but I'll mix it with RO water or my nut water. The PH has been staying steady at 6.5, I have actually worked on getting it down now, instead of up.

Either way the tap water is keeping it steady. The tap water is about 100+ ppm.

 

[Insanity566]

You want to fully mix the cal-mag in your water before adding any other nutrients. Than add your regular nutrients. And if you have to use pH up/down dilute it in small amount of ro water and slowly add the amount necessary. If the cal-mag isn't mixed well prior to adding the nutrients the solutions will start to bind to each other before they get mixed. Causing a nutrient lockout. And same with the pH adjustment. If you just add straight pH up/down to your mix the concentration will start to bind with your mix and not dispurse throughout the solution properly, before your able to mix it.
This can also cause a pH fluctuation after initial mixing. Try mixing the nutrients and let them rest for an hour and check oh before adding to res. Also depending on placement of air pump the O2 being added to the mixture can cause fluctuation of nutrient ph levels. Hope some of this helps.

 

[Dr Fish]

I don't see any plants, what ppm are you trying to stabilize the solution at? Plants are key to keeping everything in balance... The solution usually changes depending on the uptake of the plants.. Without pics it's a little hard to give any good advice...

 

[Jmonzon]

I don't see any plants, what ppm are you trying to stabilize the solution at? Plants are key to keeping everything in balance... The solution usually changes depending on the uptake of the plants.. Without pics it's a little hard to give any good advice...

Yeah, nutrients that haven't been exposed to the plants. Just sitting in the container waiting.

Really Nothing has changed, still the same exact system, same nebulas GH grow chart feeding schedule.
Maybe I'm not adding enough CalMag, or too little?

Or maybe my RO water filters are coming to the end of their life and not filtering out enough, I'll have to check, but the last time I did (2 weeks ago) it was @ 7PPM

Can't seem to wrap my head around this one.
Just wanna figure it out so I don't have to keep adding pH up and messing with the nutrients solution.

Doing a reservoir change tomorrow for 2nd week of Early Bloom, so might take some readings after everything I do and document it and try and figure this thing out.

Thanks for your help Scientific

Hello I been having the same problem and came to a conclusion that when the RO water gets air bubbles it will drop the ph.. I have an idea to place a alkaline filter to add the minerals and ph up back in my RO WATER ..I figured it will balance out and I can drink the water forever

 

[SamSmith]

I had a rough time getting my PH squared way with RO water. It takes very little ph up or down to make a significant change. I have noticed that after it gets well aerated the PH drops a bit. Using tap you battle the buffers so it is the opposite issue.

Sometimes there are buffers in the nutrients formulas. GH trio doesn't though.

 

[Delps8]

I had a rough time getting my PH squared way with RO water. It takes very little ph up or down to make a significant change. I have noticed that after it gets well aerated the PH drops a bit. Using tap you battle the buffers so it is the opposite issue.

Sometimes there are buffers in the nutrients formulas. GH trio doesn't though.

This is a very old thread that you've responded to, BTW.

Standard pH measuring instruments cannot accurately measure the pH of RO water. If you need to measure pH, add a small amount of fertilizer, calmag will do, and then test. Otherwise, any readings you get will be misleading.

 

[SmokingWings]

I been having the same problem and came to a conclusion that when the RO water gets air bubbles it will drop the ph..

Unless you're actually bubbling CO2 into the mix, I doubt that's it.

Yes, it might be an older thread and most of the early people discussing this are long gone but the answer is in the comments.

Air is being bubbled into the water which means that Carbon Dioxide is being bubbled. There is more than enough CO2 in the air, whether inside or outside the tent, to have a noticeable effect.

As the air bubble rise up through the water some of the CO2 molecules leave the air and mix in. It will start to form carbonic acid and it is enough that it will change the pH reading, sometimes within a few hours and almost always in 24 hours.

Same sort of thing happens to rain water and is why most rain is not a pH of 7 but more often in or near the 5.7 to 5.9 pH range. And, aquarium owners who might be raising some delicate specie of fish have to constantly check their water. More often than not a google search on this issue will show most of the suggested links going to aquarium web pages because it is a bigger issue for them than most gardeners.

 

[Delps8]

Yes, it might be an older thread and most of the early people discussing this are long gone but the answer is in the comments.

Couldn't agree more.

Air is being bubbled into the water which means that Carbon Dioxide is being bubbled. There is more than enough CO2 in the air, whether inside or outside the tent, to have a noticeable effect.

As the air bubble rise up through the water some of the CO2 molecules leave the air and mix in. It will start to form carbonic acid and it is enough that it will change the pH reading, sometimes within a few hours and almost always in 24 hours.

Same sort of thing happens to rain water and is why most rain is not a pH of 7 but more often in or near the 5.7 to 5.9 pH range. And, aquarium owners who might be raising some delicate specie of fish have to constantly check their water. More often than not a google search on this issue will show most of the suggested links going to aquarium web pages because it is a bigger issue for them than most gardeners.

I think this is common knowledge to growers here. As I understand it, children in the US do the experiment in grade school.

The pH drop that I has seen is not caused by CO2 bubbling through my res — I've never been able to induce a pH drop in my res by bubbling air through it. The drop in pH that drove me around the bend was caused by nutrient uptake. I've seen the pattern repeated over past two years. Conversely bubbling air through my res has not caused the pH of my res to drop. ATM, I've had my res set up and running for a few days with no plants in it and pH has risen slowly in the time.

I'm not arguing that bubbling air through the res will not result in a drop in pH-I know that's how things work. However, lacking specifics about how much air with how much CO2 for hour long, etc., etc. the fact that CO2 can induce a change in pH is of little value.

As usual, it's not the poison, it's the dose.

 

[RaidersGarden]

You want to fully mix the cal-mag in your water before adding any other nutrients. Than add your regular nutrients. And if you have to use pH up/down dilute it in small amount of ro water and slowly add the amount necessary. If the cal-mag isn't mixed well prior to adding the nutrients the solutions will start to bind to each other before they get mixed. Causing a nutrient lockout. And same with the pH adjustment. If you just add straight pH up/down to your mix the concentration will start to bind with your mix and not dispurse throughout the solution properly, before your able to mix it.
This can also cause a pH fluctuation after initial mixing. Try mixing the nutrients and let them rest for an hour and check oh before adding to res. Also depending on placement of air pump the O2 being added to the mixture can cause fluctuation of nutrient ph levels. Hope some of this helps.

I am having the same problem ph keeps dropping. I am a rookie in door grower. Only been growing indoors for 3 years. I have always added cal mag at the end. I read on-line cak mag first started doing that last week and both week i have been struggling to keep ph at 6.1. Drops down to 5.5 every 5 hours or so. So explain this to me

 

[RaidersGarden]

 

[Delps8]

i am having the same problem ph keeps dropping. I am a rookie in door grower. Only been growing indoors for 3 years. I have always added cal mag at the end. I read on-line cak mag first started doing that last week and both week i have been struggling to keep ph at 6.1. Drops down to 5.5 every 5 hours or so. So explain this to me

That much of a drop is unusual. I

CalMag, if you need to add it at all, should be added early in the process. IIRC, just after silica. Google is your friend.

Why are you adding CalMag? If you're using RO and your ferts aren't formulated for RO, then you'll have to add back the missing chemicals. Other than that, your nutes should have enough Ca and Mg.