HYDRO Water acidification with plants in flower - air pump inside the growing space

[FlyingDutchPaddy]

Hi all,

This topic/question might be especially of interest to those growing with hydroponic / DWC setups.

Since switching my lighting over to 12/12 from 24/0 3 weeks ago I've had a struggle controlling water pH levels to keep them within range.
I've observed times where before lights out, pH would be around 6.2 and after 13 hours darkness pH would drop to 5.6. I've even seen 4.8 after 20 hours since last check.

Some background.
From: http://scienceline.ucsb.edu/getkey.php?key=826
"At night, when photosynthesis is not happening, they give off much more CO₂ than they absorb."

From: http://ion.chem.usu.edu/~sbialkow/Cl...ic%20Acid.html
"The most common source of acidity in water is dissolved carbon dioxide."

With hydropinic/DWC setups most (all of us really) have some kind of system to aerate the water (typically an air pump with airstones attached bubbling air into the buckets/totes/reservoirs).

In my particular setup, I have the air pump inside my tent, with the air inlet taking air from inside the tent.

The other day the question came to me: Would the CO2 released by the plants overnight be causing the water pH to drop by such considerable amounts?
Some googling later I found the second link mentioned above.

Overnight the plants release CO2, this gets taken in by the air pump and the (higher than usual in the growing space) CO2 amounts are bubbled into the water creating carbonic acid which by itself would have a pH = 5.65.

I think that those of use already adjusting the water pH down after mixing nutrients would see this affecting the pH even more so over time.

My question to you guys:
If you've seen this problem before, how did you solve it?


Have any of you considered using a hose to let the air pump take fresh air from outside the grow space to bubble into the water, or have your air pump outside the grow space to pump it in with longer air tubes?

To test this idea I've taken a hose long enough to allow the airpump to draw intake air from outside the tent.

Will follow up with what I observe over a longer period of time.

[Toker1]

Co2 does influence ph. But not by that much. Maybe by like 1/100th. So negligible for hydro purposes.
Do you have a new system? New plastic takes time for the PH to stabilize. Once more buffers are added the PH should get into control.
Yes, run the air tubes from outside the tent to the buckets into them. That’s the best way to do it.

[FlyingDutchPaddy]

hey Toker,

its a "new-ish" system... it's been in use for about a year now.
I started a new grow in December, had lights on 24/0 for 12 weeks in Veg while I was training & quadlining two plants.
in those 12 weeks pH never really varied by much, about +- 0.3 of 6.0 over a week time

back last summer I also had an issue with pH dropping by a lot over a couple of days... when I had 4 plants growing.
Used H2O2 then... but never had the idea that CO2 might be a factor.

[Graff420]

My oh is mostly just affected by my water temp is found out seems to hover around where my water temps are so before I got the water cooler the temps would skyrocket when the lights came on along with the ph same as when it went off after it went off my phone would drop lucky I'm in a hot area so only had to worry about it getting to high but if my water temps were 68 degrees my phone would be 6.8 got a water temp and left it on 63 degrees so my water only climbs to 6.3 now and I adjust every morning

[DW2]

I agree with Toker1, don't chase the pH, especially when it is within the range of 5.5 to 6.5. Different nutrients are absorbed by the plants at different pH levels, so it it beneficial to the plants for the pH to vary some what. One can (and I speak from my nearly killing my plants during the second grow!) do damage to the plants by dumping too much pH up or down in the reservoirs to maintain a 'steady' pH level.

[Graff420]

Wow I was really high when I put that up and fked up so many words lmao but naw I adjust as needed if it get out of control as my water chiller keeps my water at 63°F so my water pH normally stays their takes about 3 to 4 days to climb to 6.3 from the original 5.5 I leave it at with the res change so normally it's stay 6.3 pH intill the next res change if I for get to turn on the water chiller tho my pH climbs to like 8.4 in 8 hours no idea why I'm guessing because water temps hit 90° to 100° but I don't know

[Toker1]

Yes... temperature and PH are related. I try to keep both stable to avoid issues.

[FlyingDutchPaddy]

Quick update.

Yesterday evening just before lights out, pH was 5.8. Just to be sure I added 2ml of pH up to the system in case the pH would drop again overnight (didnt get the chance to measure pH after that).

Came home this afternoon and checked, after 19 hours pH is 6.5.

Air pump inlet from outside the tent seems to be working well so far.

Water change tomorrow - Will see what happens!

[FlyingDutchPaddy]

just before lights out, pH = 6.5
after their night sleep 12 hrs later, pH = 6.5 ...

water change today...

[FlyingDutchPaddy]

Today's water change details....

pH = 6.2 after settling,
ppm = 980 (EC = 1.96)

entering week 3 of flower... (lights switched to 12/12 on the 9th)

on roughly 5.82 US gallons (22L)
92ml Silicon 15ml CalMag 30ml Micro 15ml Gro 30ml Bloom
Temp @ 19C & RH 48%

Air pump taking in air from outside the tent since 20th march.

Also did some leaf cutting... plants were getting bushy....

[Iammygod]

Air dissolved CO2 has very low abilities to change solution ph specially at higher EC. Respiration and electroneutrality are the main reasons of ph change. Indoor plant tend to grow equally well between ph 5.2-6.3(or even 5.2-7.5 with chelated form of iron) if each specific nutrient in the solution do not become a limiting factor.

Forms of carbon including carbonates and bicarbonates(like baking soda) and also organic acids(like citric acid) are ph buffering agent and can resist against ph change. The 1st two forms increase ph when they are added to the solution and the last one decrease ph. Adding more buffering agent to the solution prevent ph fluctuation.




last thing i like to mention is that mililiter per liter is about the volum not mass. and it is a wrong way to report concentration. The concentrations can not be calculated without knowing the solution percentage.

[FlyingDutchPaddy]

Hi @Iammygod,

I agree with you that 'reporting' concentrations as X ml to Y L is a wrong way, its not presice as it does not specify the molecular mass per volume of each nutritional element added.

However, as I'm using the DWC feeding schedule from GWE (which gives volumes in ml/Gal for nutrients), I've made a spreadsheet to give me the needed volume for nutrients based on the volume of water in my system.

https://www.growweedeasy.com/sites/growweedeasy.com/files/grow-weed-General-Hydroponics-nutrient-schedule.pdf

This is the reason i'm stating X ml Micro/Gro/Bloom for Y litres of water.

I'm using the flora trio series of nutrients, (micro for hard water). If you're interested, I can let you know what is inside each 1L bottle in order to work out how much of each nutrient is being added.

The pH down solution that I'm currently using is also by GH, and its made of "81% food grade" phosphoric acid.
My experience with this pH down solution is that it needs a while to stabilse to the desired level - typically several hours.

As for the CO2 idea...

Plant respiration -> added CO2 concentrations in tent,
air pump sucks that in, bubbles the extra CO2 into the water.
air pump does 35L/minute, 4 airstones in total.

only over the last two weeks with the plants in flower, has this issue with the pH dropping quickly come up.

CO2 is heavier than air, but with the ventilaton happening, that CO2 would be rising upwards as the air in the tent is refreshed.

it would seem, that the placement of the airpump in the tent might be a factor in this case....
Or, as I've been seeing over the last few days, having the airpump draw fresh air from outside the tent.

[FlyingDutchPaddy]

quick update,

just before lights out yesterday pH = 6.2

this morning I found pH at 6.5

have added 4 ml pH down and its now settled at 6.0.

[Iammygod]

Forget that CO2 and air pomp position. They are truly not the reason. Because of chelated forms of iron No need to lower ph when it is 6.5. Your problem is water acidification but you are adding more ph down. contradictory! How are your plant? Are they healty? What source of water do you use?

[FlyingDutchPaddy]

Iammygod,

I added a bit of pH down this time because I've seen that the pH is much more stable now that the airpump is getting air from outside the tent.
Over the last week I did not add any pH down due to the observation that pH kept dropping by a large amount during the lights out period.

Water I use comes from a private well.
starting values for ppm = 290 / pH = 7.4

The plants.... I defoliated them yesterday and they are healthy.
See pics attaced

Please see the details below for the Flora Trio that I use, with CalMag additive and Si+ (All bottles I have are 1L):

CalMag additive:
Nitrogen – 2.9%
Magnesium Oxide (MgO) - 2.5% (1.5% Mg)
Calcium Oxide (CaO) - 5% (3.6% Ca)
Iron (Fe) chelated by EDTA - 0.04%

Flora Micro (Hard water) / NPK 5-0-1
Total Nitrogen (N) - 5%
Ammoniacal nitrogen - 1.5%
Nitrate nitrogen - 3.5%
Soluble potassium (K₂O) - 1.3%
Boron (B) - 0.01%
Calcium (CaO) - 1.4%
Copper (Cu) Chelated EDTA - 0.01%
Iron (Fe) Chelated 6% EDDHA – 11% DPTA - 0.12%
Manganese (Mn) Chelated EDTA - 0.05%
Molybdenum (Mo) - 0.004%
Zinc (Zn) Chelated EDTA - 0.015%

Flora Gro / NPK 3-1-6:
Total nitrogen (N) - 3%
Ammoniacal nitrogen - 1%
Nitrate nitrogen - 2%
Phospohoric anhydride (P₂O₅) - 1%
Potassium oxide(K₂O) - 6%
Magnesium Oxide (MgO) - 0.8%

Flora Bloom / NPK 0-5-4:
Available Phosphate (P₂O₅) - 5%
Soluble potassium (K₂O) - 4%
Magnesium Oxide (MgO) - 3%
Soluble sulphur (SO₄) - 5%

Essentials Silicon+ (4ml/L) : ( I can only find the spec for Vitalink Essentials Silicone Max - at 6% - dosage 1ml / L)
SiO2 - 1.4%

[Iammygod]

What are those algae?

[FlyingDutchPaddy]

you suggesting the algae on the hydroton is the cause?

even if the water is below the net pots?

[FlyingDutchPaddy]

Update:
before lights out, pH was 6.0
this morning its was at 5.4

I've drained off 5L of water and replaced it with 4L of premixed nutrient water which was at pH 7.4

system is now at pH 6.4 , ppm 940.

trend is that ppm is falling slightly as well.

Been reading up on factors that influence pH,

A very plausable reason that pH is dropping comes from here: https://www.maximumyield.com/the-top...f-whack/2/3240
"For example, when a plant absorbs potassium ions, it gives off hydrogen ions that lower the pH."
Potassium is the K in NPK.

With my water volume being relatively small at ~ 6 US Gallons for 2 plants, could high potassium uptake be the reason for the fast drops in pH overnight?

[Toker1]

Could be. PH Could also be dropping because the plant is drinking more water than nutrients.

[FlyingDutchPaddy]

End of day update:

over the course of the day pH started off at 6.4 after changing out water and replacing it with fresh nute water.
by 1 hr before lights out, pH was 5.7

drained another 5L water out and replaced with fresh nute water, last pH 6.2 before lights out.

[Toker1]

Calcium can be a PH buffer, I think the GH line has buffers as well.
How are you keeping your deep culture water cool?

[FlyingDutchPaddy]

ambient air temp is 18 - 21 C

water will have the same temp...

[Toker1]

Might want to check on that with an aquarium thermometer. I can say for a fact that the floor of your grow room is not the same temperature as the ceiling.

[FlyingDutchPaddy]

ambient air temp in F and C

[Toker1]

Yes. This would explain the PH swings. I think water temp may be the issue. Do the roots smell unpleasant right now?

[FlyingDutchPaddy]

they didnt smell bad as such...

last time i changed water i took them out the tent as usual while i cleaned the system.
roots have brown patches on them.

then again, they have had for a few weeks now, even before switching to 12/12.
didnt interfere with pH when on 24/0.

when i took them out, i did carefully look at those brown patches...
looked slimy but not to the touch.

i'll lift them out tomorrow morning and take a pic... when i check pH again.

[Toker1]

So the nutes can leave a brownish film on the roots that easily washes off. Another way to tell is nute slime doesn’t smell unpleasant, but root rot does.

[FlyingDutchPaddy]

Been trimming roots today...

slimy, earthly smelling bits...

case of partial root rot as half the roots were brown & slimy, the other half were good.

those that were brown & slimy were also tangled with the healthy roots...

after trimming gave the roots a good wash down, back into the res.
have sensizyme in there already.

will change res tomorrow after a good clean of the system with H2O2...

fresh dose of sensizyme & also some voodoo juice to get the roots growing back.


So, i guess the question changes then to:

will partial root rot cause big pH swings, as opposed to CO2 from respiration of the plants during lights out?

[Toker1]

Yes...root rot will cause PH swings. Btw, rotting plant material releases co2 gas.

[FlyingDutchPaddy]

today's update:

Cleaned the entire system!

- let waterpump, all water tubes, airstones, more than what sits in the water of the air tubes soak for an hour in sterilising H2O2.
- cleaned out the buckets and res with H2O2
- let the assembled system run an hour with serilising levels of H2O2 water while bubbeling air.

- while i was at it, checked the quantity of water (22L) and waterpump speed to let the water level in the buckets come about 2cm below the netpots,

- drained the H2O2 water (which was clean) and added prepared water ( 5L with 90ml Si+, 10L with 37ml Ph and another 10L plain water)

- added the nutes (30ml CalMag, 90ml Si+, 30ml Micro, 15ml Gro, 30ml Bloom)

- water pH is 6.4
- ppm = 1010 (might be a bit high)

- 40ml voodoo juice, 40ml sensizym (need those trimmed roots to grow back!)

grow tent air temp = 20.6C / RH = 48%.

lets see how this progresses.

[Toker1]

Nice. Some hydroguard in the mix too might help with excessive water temps too.

[FlyingDutchPaddy]

whats the european equivalent to hydroguard?

been trying to find that since reading about it here on GWE but never found the product.

closest i think i found was the sensizym....

[Toker1]

Don’t really know. But the active ingredient is Bacillus bacteria known as Bacillus Amyloliquefaciens.
So that’s what you want to look for.