Can CO2 micro bubbles cause incorrect drop checker readings?

[xZaiox]

Hi guys,

I've googled this multiple times before, and feel that the answers given are usually too vague. Do CO2 micro bubbles alter the drop checker reading? I.e could a perfectly normal CO2 level cause a yellow drop checker by the bubbles rising up directly into the checker? Or conversely could an inadequate level of CO2 give a lime green reading? The bubbles are concentrated CO2 after all...

Would love some other opinions

 

[bazz]

Bubbles going straight up into a drop checker I would imagine will give a false reading, it's not a true picture as to the CO2 content of the water for the rest of the aquarium.
Cheers!

 

[Garuf]

Yes.

 

[Zeus.]

could a perfectly normal CO2 level cause a yellow drop checker by the bubbles rising up directly into the checker?

Yes 100%, and if enough bubbles get in could easily have clear Drop Checker (DC). A DC is best placed where the bubbles are being jetted down by the flow of water - which is normally directly opposite the filter return.

 

[MMonis]

I came across this piece of info from the 2hr aquarist website 🙄:

Many hobbyists like using drop checkers but they are not a reliable method of determining CO2 levels. Drop checkers are dependent on gaseous exchange at the exact site where the drop checker is located - this in turn depends on the water flow and position of the drop checker, quality of testing regents and color interpretation.

'Green' doesn't mean that one has good levels of CO2 in the tank. It just means that at that position, the drop checker is receiving some CO2. This result can also be skewed badly if it is in a position to capture CO2 bubbles that would otherwise be off gasses through surface water.

Because of all these reasons, the error ratio for drop checkers is too wide to be helpful in cases where it matters the most - when folks are facing problems or trying to grow more difficult plants that require optimized levels. Because most easier plants can grow in a wide range - most tanks actually do ok with low levels of CO2; but this does not mean that the device is working effectively. The true test (and often where weakness is exposed) when a hobbyist tries to grow more difficult varieties of plants that require high levels of CO2.

Many guides position the drop checker near the tank's surface, which is the worse possible position for a drop checker as it gives a false positive by capturing CO2 bubbles which would normally escape to the tank's surface water. If used at all, drop checkers should be placed near the substrate zone.

 

[Zeus.]

I came across this piece of info from the 2hr aquarist website 🙄:

Which is where a pH probe with the sensor on a lead comes in handy, as then you can move the sensor all around the tank to see any fluctuations in pH level

 

[xZaiox]

Thanks for the comments guys, this has been helpful to me.

A DC is best placed where the bubbles are being jetted down by the flow of water - which is normally directly opposite the filter return.

Thanks for this Zeus, I'm going to move my drop checker there and see if the colour changes. Do you think it's safe to assume that a lime green to yellow drop checker accompanied with a 1.3-1.4 pH drop is likely 30+ ppm of CO2? I've spent so many hours reading up on optimising CO2 but it feels like an absolute minefield of information. It seems drop checkers aren't hugely accurate and the classic 1.0 pH drop makes an assumption that the degassed CO2 is 3ppm, where it could potentially be lower.

I've pushed my pH drop to 1.7, and my fish don't go to the surface but do breathe too fast for my liking, they seem uncomfortable at that level. I'm having difficulty figuring out where to draw the line.

 

[Andy Pierce]

This at least is easy: dial back until your livestock behave unstressed.

 

[aquanoobie]

It seems drop checkers aren't hugely accurate and the classic 1.0 pH drop makes an assumption that the degassed CO2 is 3ppm, where it could potentially be lower.

Hi @xZaiox
Degassed water can have anything between 0.5 to 5 or 8 ppm of CO2. Therefore 1 pH drop can have 5 to 50 or 80 ppm of CO2. It's like rolling the dice.

 

[Zeus.]

Do you think it's safe to assume that a lime green to yellow drop checker accompanied with a 1.3-1.4 pH drop is likely 30+ ppm of CO2?

No a 1.0pH drop is approx 30ppm.

It seems drop checkers aren't hugely accurate

DC are accurate, but only slow the pH and relative [CO2] in the air space between the tank water and the DC solution. If CO2 bubbles get into the DC then DC solution will show a false pH/[CO2]. Which is why I would always advise doing a pH profile in combination to the DC colour change, plus watch livestock carefully.

I've pushed my pH drop to 1.7

The biggest pH drop my livestock could handle was about 1.4pH and the DC was very light yellow to clear. I was also using CO2 reactors so there was no CO2 bubbles in tank

Hi @xZaiox
Degassed water can have anything between 0.5 to 5 or 8 ppm of CO2. Therefore 1 pH drop can have 5 to 50 or 80 ppm of CO2. It's like rolling the dice.

I would disagree with that, as [CO2] in water will follow Henrys law, we have our tanks at a relative constant temp and the air pressure is relatively constant. The atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp (@dw1305 / @X3NiTH)

 

[aquanoobie]

I would disagree with that, as [CO2] in water will follow Henrys law, we have our tanks at a relative constant temp and the air pressure is relatively constant. The atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp

Hi @Zeus.
I agree with everything you said if we were to keep our tanks outside, but some homes don't have much ventilation in hot seasons with air conditioning or in winter with heating. The CO2 value varies from ~400 to ~2500 ppm which will affect degassed equilibrium levels. Below is a picture of a CO2 meter on a table at the White House Correspondent's Dinner on April 30th 2022, two days ago. It reads 2 233 ppm of CO2 in the room. These levels are not unusual.



Next issue is the actual equilibrium. In Diana Walstad's book is a referenced scientific paper that says the equilibrium is 0.5 ppm of CO2 at the traditional ~400 ppm outside.

 

[Zeus.]

CO2 value varies from ~400 to ~2500 ppm which will affect degassed equilibrium levels

Agree

Below is a picture of a CO2 meter on a table at the White House Correspondent's Dinner on April 30th 2022, two days ago. It reads 2 233 ppm of CO2 in the room. These levels are not unusual.

any thing above 600ppm CO2 is unsuitable for humans over any length of time IMO. You need to open a window or turn up the heat exchange to acceptable levels

equilibrium is 0.5 ppm of CO2 at the traditional ~400 ppm outside.

Which it could be as I didn't check 😬

 

[Simon Cole]

Then there is the factor that any mist will collect on the under-side of leaves where stomata are abundant.
Milli-bubbles - 1 mm to 1μm
Micro-bubbles - 10 μm to 50 μm
Nano-bubbles < 200 nm
Seems odd that these classes do not overlap, but then I do make the rules up.
Stomatal pores could be between 30 μm and 150 μm in diameter. Stomatal density could be between 30 and 300 per mm-squared. Sorry this is vague, but it varies from species to species and adaptation to submersion.
I am guessing that milli-bubbles get trapped in the stomatal opening. Nano-bubbles and some micro-bubbles can probably enter the mesophyll freely. Drop checkers can probably trap and collect all three bubble classes.

I am sure that the concentration of dissolved carbon dioxide is important, but perhaps the gas bubbles are also very useful to living plant tissue. I guess that if you wanted to get accurate drop checker results for fully dissolved carbon dioxide, then you would need to remove the bubbles, and that this could potentially be degassing your "diffused" carbon dioxide in the same process. It makes me wonder how feasible it is to measure dissolved carbon dioxide levels without using the pH drop technique. Moreover, whether you use a drop checker or a pH drop, I wonder whether the dissolved carbon dioxide concentration would matter that much if bubbles are effective nutrient transporters anyway. Overall the drop checker is just a visual index and the pH drop is a measure of dissolved carbon dioxide potential. Some logic would apply if you used a grade of fine filter paper over your drop checker matching the size of the average stomatal opening, like Whatman grade 4; but you could alternatively go for something finer like Whatman grade 5; so why not use several filtered drop checkers so that you know the impact of gas bubble size if you were interested. Also, it is likely that fish gills trap or absorb carbon dioxide gas bubbles, so this is also relevant.

My own view is that 'pearling' is also very useful to observe. Anecdotal evidence regarding visual cues like drop checkers are still very useful. Most of this is fairly paradoxical, but if I had to pick, I would say do all three because gas bubbles matter.

any thing above 600ppm CO2 is unsuitable for humans over any length of time IMO

Cheers for this post. I am getting swollen feet (and far worse symptoms) and I am convinced that I am close to 4,000 ppm sometimes, so I'll ask my doctor for a kit because they are coming around soon.

 

[Zeus.]

Cheers for this post. I am getting swollen feet (and far worse symptoms) and I am convinced that I am close to 4,000 ppm

TBH I was unaware myself till I googled it last night. But ventilation in dwellings is so important to our well being esp with increasing energy cost. Planning on fitting a ventilated heat exchange/recovery system on present house as I remove all the drafts and trickle vents.

 

[dw1305]

Hi all,

the atmospheric [CO2] (although slowly increasing) is still relatively constant. So therefore once the water has fully degassed/gassed for the same temp and atmospheric pressure the [CO2] in water will be the same all around the planet which I think is approximately 4ppm at room temp (@dw1305 / @X3NiTH)

We never found where the 3 ppm figure <"actually came from">. I had a look at the lab CO2 monitor earlier today and it was 562 ppm CO2.

cheers Darrel

 

[aquanoobie]

I'm not a CO2 user, but I think you are right, the level of dissolved CO2 depends upon Henry's law, and if you assume 400 ppm CO2 in the atmosphere, standard pressure (1013mb) and a temperature of 20oC, then you have 1.35 x 10-5 mols l-1 of CO2 dissolved.

The RMM of CO2 is 12 + (16*2) = 44 (44g of CO2 in ), and if you work that out as ppm, it comes to ~0.6ppm (0.594ppm). The reason that that level is higher than the quoted 0.55ppm is just because the level of atmospheric CO2 has risen.

We have a CO2 monitor in the lab. and that usually sits at about 600ppm, but it is still along way from there to the dissolved 3 ppm quoted.

The only reference I could find for the 3ppm datum was the experimental work that George and Karla Booth did in the 1990's <"CO2 loss in large aquariums">.

cheers Darrel

Hi @dw1305
This is enlightening, thank you! What would it take to make you curious enough to calculate 2500 ppm CO2?

 

[dw1305]

Hi all,

What would it take to make you curious enough to calculate 2500 ppm CO2?

Strange you should mention that, but <"we have a thread">.

cheers Darrel

 

[aquanoobie]

Hi all,

Strange you should mention that, but <"we have a thread">.

cheers Darrel

Hi @dw1305
What I am looking for is how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2. Sorry for the confusion.

 

[dw1305]

Hi all,

Hi @dw1305
What I am looking for is how much in ppm CO2 is going to have degassed water at atmospheric 2500 ppm CO2. Sorry for the confusion.

I can <"work that out">.

Cheers Darrel

 

[xZaiox]

The biggest pH drop my livestock could handle was about 1.4pH and the DC was very light yellow to clear. I was also using CO2 reactors so there was no CO2 bubbles in tank

Zeus, can I ask what symptoms your livestock displayed when the CO2 was too high? I'm wanting to be extra vigilant and know what signs to look out for. I've read reports from people before who have claimed their only symptom was fish death, which is a worrying thought to me! I'm also confused how I was able to drop the pH 1.7 in the first place, from everything I have read, this sounds like in theory it should be a substantial overdose. As I was raising it, I kept thinking "surely they're going to head to the surface soon?".

Also thanks again to all those who have commented