CO2, KH and alkaline substrate

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
Will alkaline substrate and rock interfere with CO2 readings using the KH - pH chart?

I have dialed up CO2 by 50% using Tunze CO2 reactor from 1 bps to 1.5 bps but could not detect a change in CO2 according to the KH-pH chart. Note that 1 bps in the Tunze reactor is about double to triple the bubble size of a regular bubble counter from the regulator

https://www.ebay.com/itm/Tunze-USA-...Reactor-New-/142549640309?hash=item21309ee475

My 75 gal pre and post CO2 pH are 7.6 and 7.0, respectively, regardless of the CO2 injection rate. But I am certain CO2 is getting into the system as I can observe increase in plant growth rate and faster dissolution of my limestone rocks. I have dolomite substrate which is likely dissolving away faster but I won't be able to detect.

My tap KH is around 4 and tank KH is consistently 5. My tap GH is around 5 and tank GH ranged between 10 to 15. I do not add GH, and apparently the alkaline substrate and rock affect the GH, but barely the KH.

I am wondering if alkaline substrate and rock can interfere with CO2 readings based on the KH-pH chart. I also have a CO2 drop checker but the color stays nearly the same, always blue green.
 
Last edited:

Greggz

Lifetime Members
Lifetime Member
Jan 6, 2016
448
578
93
Will alkaline substrate and rock interfere with CO2 readings using the KH - pH chart?

I have dialed up CO2 by 50% using Tunze CO2 reactor from 1 bps to 1.5 bps but could not detect a change in CO2 according to the KH-pH chart. Note that 1 bps in the Tunze reactor is about double to triple the bubble size of a regular bubble counter from the regulator

https://www.ebay.com/itm/Tunze-USA-...Reactor-New-/142549640309?hash=item21309ee475

My 75 gal pre and post CO2 pH are 7.6 and 7.0, respectively, regardless of the CO2 injection rate. But I am certain CO2 is getting into the system as I can observe increase in plant growth rate and faster dissolution of my limestone rocks. I have dolomite substrate which is likely dissolving away faster but I won't be able to detect.

My tap KH is around 4 and tank KH is consistently 5. My tap GH is around 5 and tank GH ranged between 10 to 15. I do not add GH, and apparently the alkaline substrate and rock affect the GH, but barely the KH.

I am wondering if alkaline substrate and rock can interfere with CO2 readings based on the KH-pH chart. I also have a CO2 drop checker but the color stays nearly the same, always blue green.
If you truly are driving the pH down from 7.6 to 7.0, then a blue green drop checker would be correct. That's only a .6 drop, and you won't see it fully green until you get to about 1.0.

And if your pH is the same regardless of the CO2 injection rate, then something is probably wrong with your injection. Do you have a calibrated pH meter/monitor? If not, I would get one. Then I would really crank up the CO2 and see if the pH is dropping. If it's not, you have other issues.

And while the substrate/rocks may affect the KH, it does not change the relationship between KH/pH/CO2. If the KH rises, then so will the pH. And if the GH rises, it has no effect at all on the KH.
 

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
I don't have a pH meter, just the API pH test kit. I was assuming that a 50% increase in bps is a lot and should reflect in the pH readings, but apparently not. So it could be another bad test kit. I will crank up CO2 even more to see if it will make a difference.
 

Greggz

Lifetime Members
Lifetime Member
Jan 6, 2016
448
578
93
I don't have a pH meter, just the API pH test kit. I was assuming that a 50% increase in bps is a lot and should reflect in the pH readings, but apparently not. So it could be another bad test kit. I will crank up CO2 even more to see if it will make a difference.
I tested the API pH test against a calibrated meter one time, and let me tell you it was not even close. Don't trust that at all. You could easily be having much less pH drop than you think. And 1 or 2 BPS in a 75 is nothing. It should be closer to a constant stream to get any meaningful drop.

And when you are fine tuning a tank, having a correct pH reading is a must, as CO2 concentration is one of the first things you want to get right. A cheap pH meter and some calibration solution will be your friend, and well worth the small investment in the long run. I can't imagine being without one.
 

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
I tested the API pH test against a calibrated meter one time, and let me tell you it was not even close. Don't trust that at all. You could easily be having much less pH drop than you think. And 1 or 2 BPS in a 75 is nothing. It should be closer to a constant stream to get any meaningful drop.
.

It’s another one of the test kit that can’t be trusted. It’s not 1 or 2 bps. It’s more like 2 to 4 bps on a regulatar counter as the bubble size in the Tunze reactor is twice to triple the size. My regulator counter fluid has dried up and if it were still readable, it’s too fast for me to read.
 

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
I still have not been able to bring down the pH by increasing the bps or extending the CO2 warm up period. The pH will bottom out at 7 no matter what I did.

I think my buffering dolomite substrate and rock has something to do with it. CO2 can eat up kH, but my kH stays steady at 5, suggesting that kH is quickly replenished. But I believe CO2 is effectively getting into the system as I witnessed faster plant growth and erosion of my limestone rock.

I do not know precisely my initial pH as my low range API chart max out at 7.6. My high range API is not helpful either as the color between 7.4 to 8.0 are nearly indistinguishable. So my true initial pH can be anywhere between 7.6 to 8.0. I need a good PH meter and calibration fluid, and what do you recommend.

Please explain why it is advised to drop the pH by 1 point. The CO2 chart has 2 dependent variables, pH and kH, and the outcome is independent of the initial condition. According to the chart or the Roto calculator, at KH 5, I need to reach pH 6.7 to attain 30 ppm CO2 regardless of the initial pH.
 

Greggz

Lifetime Members
Lifetime Member
Jan 6, 2016
448
578
93
Please explain why it is advised to drop the pH by 1 point. The CO2 chart has 2 dependent variables, pH and kH, and the outcome is independent of the initial condition. According to the chart or the Roto calculator, at KH 5, I need to reach pH 6.7 to attain 30 ppm CO2 regardless of the initial pH.
Here's why. At a KH of 5, you would expect your degassed water to be at pH 7.7. That is with a normal ambient CO2 level of 3 ppm. So in theory, a drop to pH 6.7 from water at KH 5 should provide 30ppm CO2.

Now, that is in theory. Your KH could be more like 4.5 or 5.5, and your ambient degassed pH could be anywhere from about 7.5 to about 7.9, depending on the true KH and how much CO2 it's holding.

Confused? Yes that is why it really is best to get a pH probe and calibration solution. First find your actual degassed pH, then record the drop from there. And by the way, I think you will find many who go well below a 1.0 drop, closer to 1.3 or 1.4 in many cases.

As to not being able to drop lower than 7.0 pH, I wouldn't trust your test kit at all for that. Just not nearly precise enough. First get a pH probe, then really crank up the CO2 (like a steady stream, not counting bubbles), and monitor the pH over a few hours with a probe. I'm guessing you can drop it further than you think.

And one last thing. I would use of the calculators like Zorfox or Rotala Butterfly and not the chart. It will make more sense once you get things sorted out a bit.

Hope that helps and makes some sense.
 

Phishless

Lifetime Member
Lifetime Member
Jul 13, 2017
1,116
970
113
Arnold, MD
If you order a pH pen from like "The Ebay" you will no longer need to distinguish between API colors.:D
As @Greggz stated at least a 1.0 drop from degassed water to water tested during premium photoperiod.
If I tried to count bubbles I'd go bananas.o_O
 
  • Like
Reactions: Greggz

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
If you order a pH pen from like "The Ebay" you will no longer need to distinguish between API colors.:D
As @Greggz stated at least a 1.0 drop from degassed water to water tested during premium photoperiod.
If I tried to count bubbles I'd go bananas.o_O

The 1 pH drop makes sense to me now. It turns out that mathematically, degassed water pH drop of 1.0 will yield 30 ppm CO2 precisely.

This works beautifully as I don't even need to know or determine kH precisely. It drove me banana trying to match API colors. What pH pen do you recommend, and do you have to order calibration fluids separately?

I assume ppm refers to dissolved CO2, not free CO2 as I can see micro bubbles coming out of the reactor. So the chart underestimates total CO2 as both dissolved and free CO2 are available to plants.

My degassed pH is 7.8, based on API color jump from 7.4 to 7.8 in the high range chart. So I need to bring the pH down to 6.8, awaiting a precise pH meter to see if I can achieve it.

I discovered a quick way to measure degassed pH without waiting for 24 hour. Fill the test tube with tank water and API test liquid. Read the current pH. Cap the test tube and shake vigorously a few times. Uncap it and let the rising bubbles foam up. Tap lightly to dissipate the foam. Repeat the process a few times to drive out all dissolved gases. You can see the color deepens in each iteration and the final stable color is the degassed pH.
 

Phishless

Lifetime Member
Lifetime Member
Jul 13, 2017
1,116
970
113
Arnold, MD
Ebay usually has some set for around $20 pH pen, TDS pen, and a 7.0 calibration fluid.
They are always changing color or name, who knows.
I have found that a pen works best if kept wet all the time, like in a cup with water, any water.
Life on these pH pens I found to be about 2 years then they get wonky.
TDS pens seem to last indefinite if not broken.

I drop an air stone in a cup of tank water for about 30 minutes to de-gas.
 

Greggz

Lifetime Members
Lifetime Member
Jan 6, 2016
448
578
93
I discovered a quick way to measure degassed pH without waiting for 24 hour. Fill the test tube with tank water and API test liquid. Read the current pH. Cap the test tube and shake vigorously a few times. Uncap it and let the rising bubbles foam up. Tap lightly to dissipate the foam. Repeat the process a few times to drive out all dissolved gases. You can see the color deepens in each iteration and the final stable color is the degassed pH.
I wouldn't rely on that method if I were you. Like Phishless said above an air stone works well.

And if just leaving it sit out, I would make it more like 2 or 3 days. I've done so and it keeps degassing for much longer than you would think.

And by the way, tap water KH doesn't necessarily stay the same all the time. It can fluctuate. So getting into a habit of testing your degassed water periodically is a good idea. Or at least checking KH to see if there is any meaningful change.
 

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
I tried the method a few times and compare the color after letting the test tube water sit overnight. The color is the same, so the method is accurate enough within the precision of API test kit.

Shaking accelerates the degassing process, sort like shaking a soda bottle. Try it. You can falsify the method by control experiment with a pH pen which provides greater precision Degassing doesn’t mean degassing everything, just reaching new equilibrium with atmospheric gas composition. Shaking accelerates faster equilibrium.

I tested my tank water kH many times and it has been constant at 5 every time. I think the buffering substrate helpes stabilize the kH. If you dose water with kH, it may not be as stable because CO2 can eat up kH. I don’t expect my tap water stable as parameters vary with season, runoff and mixing of water sources.
 

tiger15

Member
Aug 12, 2017
240
82
28
69
NJ
Check this YouTube for explanation.


I converted my hard water cichlid tank to planted cichlid and keep buffering dolomite substrate and limestone rock.
 

Greggz

Lifetime Members
Lifetime Member
Jan 6, 2016
448
578
93
I tried the method a few times and compare the color after letting the test tube water sit overnight. The color is the same, so the method is accurate enough within the precision of API test kit.

Shaking accelerates the degassing process, sort like shaking a soda bottle. Try it. You can falsify the method by control experiment with a pH pen which provides greater precision Degassing doesn’t mean degassing everything, just reaching new equilibrium with atmospheric gas composition. Shaking accelerates faster equilibrium.

I tested my tank water kH many times and it has been constant at 5 every time. I think the buffering substrate helpes stabilize the kH. If you dose water with kH, it may not be as stable because CO2 can eat up kH. I don’t expect my tap water stable as parameters vary with season, runoff and mixing of water sources.
Uhhhh....Okey Dokey
 

Phishless

Lifetime Member
Lifetime Member
Jul 13, 2017
1,116
970
113
Arnold, MD
I'll only saying this.
As of lately, after getting my pH probe calibrated, while testing KH.
pH goes up and down during the daily CO2 cycle and no change to KH readings for 4 days!o_O

Panda Cory's are cute, ain't they!:D
 
  • Like
Reactions: Greggz

Allwissend

Super Moderator
Staff member
Moderator
Lifetime Member
Jun 20, 2016
581
294
63
www.intuitiveaqua.net
In this case showing a video of nice fish, green plants, shaking hands and vials does not really help explain what he is talking about. Here is a website that might clarify some of the equations he speaks about :
http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic Acid.html

But after 2:40 he pretty much losses chemistry and goes into wishful thinking.
As you can see all the reactions of CO2 with water are reversible. In an open system such as our aquariums the moment you stop adding extra CO2, you start going back towards equilibrium with the atmosphere. In other words, with CO2 injection you go from left to right in the equations in the link; without extra CO2 you go back. While the ability to buffer acids is somewhat lowered ( because you are adding an acid and pH is lowered), the KH or concentration of stable carbonates and bicarbonates in the water is not touched at all. The pH before CO2 and after CO2 (degassed) is the same, and so is the KH.

I have aquariums from KH of 15 to KH of 0, and I can also tell in practice that CO2 does, unfortunately, not lower KH. I had to pay for a RO unit and pay for the extra water it uses. I bet that buffering substrate he has in the tank has more to do with the lowering of KH than anything. More so if it is new.

I love his logical conclusion from "CO2 eats buffer" : "If you have hard water ... use CO2 and you will experience success with most every plant..." ...questions?
 
Last edited: