Co2 drop checker vs ph measure

[Mattsdoneitagain]

Hi all. Being quite new to co2 just wondering how you all measure it ?
I know that as hobbyists we can’t measure ph accurately so this is how I’ve been doing it , can someone out there please tell me if I’m in the ball park?
So I’ve taken ph readings from the off gas state so now I have a base line reading let’s say 7.8 I’ve set my co2 so that lights come on with a 1ph drop to 6.8 and switch off at 6.6 to compensate the photo period which is 3hrs morning and 4hrs evening. I’m not having any issues just wanted to know peoples thoughts on the subject not being from any scientific background I do find the subject confusing and fascinating.
Also how anal are the community about readings I find myself being supper critical to the point on the digi pen and I’m really thinking I’m being a bit finicky.

Thanks
Matt

 

[Zeus.]

IMO the actual pH reading when injecting CO2 is irrelevant, as we are just using the pH reading as a proxy for CO2 concentration. I have even reached the stage where a rarely calibrate a pH pen. For injecting CO2 a DC (Drop Checker) and the pH change during the photo period is all we need for getting a pH profile.

Knowing the base pH can be helpful as it can help in choosing the correct Fe Chelate, however your local water supplier provides this information, Some local water supplies vary there composition over the seasons and it is blended to meet certain parameters, if you tap water is soft then the pH is low and the actual pH becomes pretty much irrelevant again IMO.

It can be a minefield as there are so many variables to consider, which is one of the reasons professional aquascapers tend to favour using RO water and remineralize it so it's the same all the time at every water change.

 

[dw1305]

Hi all,

I’m not having any issues just wanted to know peoples thoughts on the subject not being from any scientific background I do find the subject confusing and fascinating.

It is quite a problematic area, even if you have some scientific background. The drop checker works because there is an experimentally derived relationship between carbonate hardness (dKH or alkalinity) and pH. The design of the drop checker, with an air gap, means that only gases (and in this case CO2) can diffuse into the drop checker solution, which contains a solution of 4dKH hardness and a narrow range pH indicator (Bromothymol Blue).

Cheers Darrel

 

[Mattsdoneitagain]

Hi thanks for that 👍
So if the base line means not a lot i could just go off my tap water ph as a start point ?
I’m also going to set up a rain water bucket as my gf is not happy about the water bill 😂 so that will affect it I suppose.
I’m actually EI dosing but it looks like I’m diving down a rabbit hole here I think.
I’ve based my EI off rotala calculations but I assume it doesn’t take into account my tap tds ? Because it can’t tell , That must be for ro water only ? I have only just this min thought about it.

Thanks

 

[Mattsdoneitagain]

Hi all,

It is quite a problematic area, even if you have some scientific background. The drop checker works because there is an experimentally derived relationship between carbonate hardness (dKH or alkalinity) and pH. The design of the drop checker, with an air gap, means that only gases (and in this case CO2) can diffuse into the drop checker solution, which contains a solution of 4dKH hardness and a narrow range pH indicator (Bromothymol Blue).

Cheers Darrel

Ok thanks I understand a little bit and can pick things up quite quickly I get the relationship between them and the slow reaction time, but I suppose what I’m getting is I keep reading about this 1 ph drop between the no gas’s and gas on and lights on. But surely I need a starting reference?
I’m not sure I get it at all now 😂

Matt

 

[LMuhlen]

There will always be uncertainties with the CO2 estimations when using these available methods.

From what I managed to understand, hopefully correctly, of the logic behind the tests:

The pH drop comes from the notion that a 1pH drop means an increase of 10x in acidity. With the pH drop being associated only to the increase in carbonic acid, which is proportional to the CO2 concentration, we derive that there was a 10x increase in CO2. Issues are that we don't know what the base concentration is. Supposedly, the equilibrium with the atmosphere alone would bring us to ~0.5ppm CO2, so the 1pH drop would get us to 5ppm only. At some point, the notion that the base CO2 concentration is 3ppm, maybe because of bacterial activity, maybe something else, but that is a big uncertainty, since it gets multiplied by 10.

Also, and this part is very obscure to me, I think that the proportion of CO2 to carbonic acid changes as the pH changes, because of the whole bicarbonate - carbonic acid equilibrium at different pHs. This should be a minor change, possibly, but it is different depending on the starting point of the 1pH drop. If this is true, you would need slightly different pH drops for alkaline water and for acid water, to get the same increase of CO2.

As for the Drop Checker, other than the inherent delay in the response, due to the slow speed of diffusion of the water CO2 to the air gap and then again to the pH measuring solution, there could be uncertainties on the precision of the KH of the solution, and we know that as the solution ages it changes the reading, so for sure there is something happening there as well. And there is the uncertainty associated with the color reading.

The drop checker doesn't need a base reference to read the CO2 concentration, it is an absolute reading.

 

[Mattsdoneitagain]

As for the Drop Checker, other than the inherent delay in the response, due to the slow speed of diffusion of the water CO2 to the air gap and then again to the pH measuring solution, there could be uncertainties on the precision of the KH of the solution, and we know that as the solution ages it changes the reading, so for sure there is something happening there as well. And there is the uncertainty associated with the color reading.

The drop checker doesn't need a base reference to read the CO2 concentration, it is an absolute reading.

That’s exactly why I was trying the other method ph measure, I do get a nice lime green which tallies with my ph measurements and don’t have any issues as regards to plants or fish.
Just wanted more understanding at least I know more than when I started.

Thanks

 

[dw1305]

Hi all,
I'm <"not a CO2 user personally">, but I know a bit about the <"practical difficulties of pH measurement"> and I wouldn't rely on a pH meter, but I would be happier to use a drop checker.

Supposedly, the equilibrium with the atmosphere alone would bring us to ~0.5ppm CO2, so the 1pH drop would get us to 5ppm only.

<"Almost 0.6 ppm now">, due to the rise in <"atmospheric CO2 levels">.

At some point, the notion that the base CO2 concentration is 3ppm,

It <"comes from"> the work of <"George Booth"> at <"the Krib"> - <"CO2 ``FAQ''">. There are plenty of papers on natural CO2 levels in freshwater, but they nearly all rely on the carbonate equilibrium (and temperature) to estimate the CO2 level - <"A 30-year dataset of CO2 in flowing freshwaters in the United States - Scientific Data">, rather than actual CO2 measurements. This really just reflects the difficulty of <"measuring dissolved CO2 directly">.

The log10 nature of the pH scale, and how that relates to CO2 content, is described by @hax47 recently <"Confusion concerning 0dKH and nitrification"> and @Jose in this older post <"Question about pressurised CO2 and water disturbance">.

which contains a solution of 4dKH hardness and a narrow range pH indicator (Bromothymol Blue).

I should have done this bit as well, the colour change occurs as the bromothymol blue becomes "protonated" (gains an H+ ion). <"Deprotonated "bromothymol blue" is blue in colour"> and protonated yellow and when you have a green colour? You have a mixture of blue and yellow.

cheers Darrel

 

[MichaelJ]

<"Almost 0.6 ppm now">, due to the rise in <"atmospheric CO2 levels">.

It almost makes it a "mystery" to me how we can grow plants, cultivate bacteria etc. in our low-tech tanks if the CO2 equilibrium is only 0.6 ppm...

However this is not a day to quibble about CO2 in our aquariums... but a day to ingest CO2 from Guinness Draught. Happy St. Patrick's Day ☘️

Cheers,
Michael

 

[Little]

but a day to ingest CO2 from Guinness Draught. Happy St. Patrick's Day ☘️

And Nitrogen! It’s what makes it so creamy. Happy St Patrick’s Day 🎉

 

[Andy Pierce]

Also, and this part is very obscure to me, I think that the proportion of CO2 to carbonic acid changes as the pH changes, because of the whole bicarbonate - carbonic acid equilibrium at different pHs.

No it does not, although this is a common misconception. There is no pH dependence on the ratio of dissolved CO2 to carbonic acid. The clue is in the chemistry where the equilibrium CO2 + H2O <-> H2CO3 does not have either an H+ or OH- component.

 

[John q]

That’s exactly why I was trying the other method ph measure, I do get a nice lime green which tallies with my ph measurements and don’t have any issues as regards to plants or fish.
Just wanted more understanding at least I know more than when I started.

Thanks

It's a tangled mess, but it doesn't need to be.

The best advice I can give to anyone starting out injecting C02 is this.
Use 3 methods of calculating co2 levels. Ph change, drop checker colour, and the most important measure by far... how are the fish reacting.

Ph meters are accurate enough for our needs, the ph change is the important bit. Whether or not it was lab grade calibrated is imo, a distraction.
Monitor the ph and look at the dc, make photographic notes how the dc changes in relation to the ph. Obviously understand the dc lags by 1 ~2 hrs.

By doing this you will quickly learn to guesstimate the tank ph based on the dc colour, or guesstimate the dc colour based on ph meter readings.

I've just eyballed both dc' in my tank, I guessed one was sitting at 6ph, the other at 5.5. I wasn’t that far out. 😆

 

[LMuhlen]

No it does not, although this is a common misconception. There is no pH dependence on the ratio of dissolved CO2 to carbonic acid. The clue is in the chemistry where the equilibrium CO2 + H2O <-> H2CO3 does not have either an H+ or OH- component.

But what about the acid vs bicarbonate equilibrium? They all need to work together, right? If at a different pH the acid turns into bicarbonate at varying proportions, that will change the pH drop measured, won't it? Although, now that I think of it, if it dissociates and turns into H+ + HCO3-, then there is a free proton, while when it was H2CO3 there wasn't, so the acidity comes from forming bicarbonates?

Me Chemistry!

 

[dw1305]

Hi all,

It almost makes it a "mystery" to me how we can grow plants, cultivate bacteria etc. in our low-tech tanks if the CO2 equilibrium is only 0.6 ppm...

I'm going to guess that the CO2 concentration is higher than the <"theoretical value derived from Henry's Law">.

I know with wastewater treatment (and aquaculture) one of the issues is getting the CO2 to outgas efficiently <"https://ag.arizona.edu/azaqua/ista/...2006/8 Gas Transfer/Degassing/CO2 Control.pdf"> & <"https://www.sciencedirect.com/science/article/pii/S0144860900000340">.

cheers Darrel

 

[Andy Pierce]

if it [H2CO3] dissociates and turns into H+ + HCO3-, then there is a free proton, while when it was H2CO3 there wasn't, so the acidity comes from forming bicarbonates?

Yes, that's right and the dissociation reaction has a strong pH dependence.

 

[hax47]

It almost makes it a "mystery" to me how we can grow plants, cultivate bacteria etc. in our low-tech tanks if the CO2 equilibrium is only 0.6 ppm...

Unless you keep the aquarium outside in the backyard, you probably will never have 0.6 ppm equilibrium CO2 in the aquarium (which value corresponds to about 400 ppm CO2 in the air). Here are some recordings from a project in progress... Continuous CO2 measurements in room air where I keep some of my aquariums. The room CO2 levels touch the 600 ppm range only for a short period when no one is at home, otherwise, it resides over 1000 ppm:

 

[dw1305]

Hi all,

The room CO2 levels touch the 600 ppm range only for a short period when no one is at home, otherwise, it resides over 1000 ppm:

We have CO2 monitors <"in the teaching lab">. They rarely get to 1000 ppm, but it is probably better ventilated than an average house.

cheers Darrel

 

[Andy Pierce]

Unless you keep the aquarium outside in the backyard, you probably will never have 0.6 ppm equilibrium CO2 in the aquarium (which value corresponds to about 400 ppm CO2 in the air). Here are some recordings from a project in progress... Continuous CO2 measurements in room air where I keep some of my aquariums. The room CO2 levels touch the 600 ppm range only for a short period when no one is at home, otherwise, it resides over 1000 ppm:

For funzies I picked up an inexpensive CO2 monitor as well. In our old draughty house it usually reads between 600 and 800 ppm when we're in the same room. It occasionally gets over 1000, but that's unusual.

 

[hax47]

For funzies I picked up an inexpensive CO2 monitor as well. In our old draughty house it usually reads between 600 and 800 ppm when we're in the same room. It occasionally gets over 1000, but that's unusual.

Probably the CO2 levels are very dependent on the occupancy, ventilation, and insulation. We have a recently built well-insulated home and the occupancy is two adults, three adolescents, and two larger breed dogs. The air volume in the house should be important too.

I guess, the usually accepted in-room equilibrated CO2 value of 2-4 ppm in water suggests that the CO2 concentration in homes above 1000 ppm is not uncommon.

 

[Andy Pierce]

I guess, the usually accepted in-room equilibrated CO2 value of 2-4 ppm in water suggests that the CO2 concentration in homes above 1000 ppm is not uncommon.

I mostly think the usually accepted low-tech CO2 value of 2-4 ppm is just wrong actually. I'm reasonably sure a drop checker using a 0.25 dKH bromothymol blue pH indicator solution would do a pretty good job of sorting out these lower CO2 concentrations, but making such an indicator solution correctly would not be a trivial undertaking.