• Welcome to ScapeCrunch!

    We are a friendly, online community of people interested in planted aquariums. We support and help each other learn and grow. It is our sincere hope that you will join us and find our tight-knit community valuable and fun!

    ScapeCrunch is different than Facebook Groups. Here's how:

    • It is a place where you can make long-term friends in the planted aquarium hobby and have long, multi-day talks on specific subjects.
    • Unlike social media, online communities like ScapeCrunch are much better at curating collective knowledge and in fostering deeper relationships.
    • They lend themselves better at long-form discussions.
    • You can maintain a thread on your personal aquarium with pictures and details. Other members can comment, help and ask questions. You can do the same with their Member Tank threads.

    Where Facebook is more like a large city-wide party, ScapeCrunch is more like your neighborhood bar "where everybody knows your name. And they're always glad you came." It's always fun to go to large parties but it's at the local bar that you feel people really know you. The great part is that you can and should go to both!

    Please consider joining to become a full fledged member of our growing community of planted aquarium obsessed enthusiasts. Let's grow together!

    Join Us!

How long does your CO2 tank last?

Reducing surface agitation doesn’t necessarily mean reducing flow
This, I’ll aim my nozzles lower as I have them aimed up. The display water spills into the back chamber on 2 sides ( left and right). It’s like a miniature water fall on both sides where the display water enters the filter socks. Quite noisy to be honest. The water then runs through baffles through the back chamber which creates more surface agitation. I also have a skimmer running on the display side..
 
This is the surface flow on the left side of my tank. Right side would be similar if it wasn't full of hygrophila lol. There's enough flow to hit the lower layers of the tank.

od39SqLh.png


sump
 
Acrylic top brace math:
Top: 72 x 24 = 1728 sq in
- Access Holes: 2x 8 x 23 = 368 sq in
- Access Holes: 2x 2.25 x 15.75 = 70.875 sq in
= 1289.125 sq in

74.6% of My surface area is covered

It's garbage for scaping/maintenance work but I wont deny that it helps save a lot of co2

Don't really need to do the math on the sump. All the plumbing run through bulkheads and access holes have glass lids. Painter's tape on the one hole where cables come out.
 
Way too much effort there 😂 with my sump I have minimal to no turbulence at all because my Poret foam sponges act as the baffles. Water enters below the surface and then gently makes its way through the sponges to the return. CO2 output on the cerges exits right to return pump where I have a cylinder covering the intake so that all the co2 rich water is sucked up by the pump. I contemplated doing what you did but I just couldn’t be bothered, would require a lot of cutting and just a PIA for maintenance as you’ve already expressed.
 
Way too much effort there 😂 with my sump I have minimal to no turbulence at all because my Poret foam sponges act as the baffles. Water enters below the surface and then gently makes its way through the sponges to the return. CO2 output on the cerges exits right to return pump where I have a cylinder covering the intake so that all the co2 rich water is sucked up by the pump. I contemplated doing what you did but I just couldn’t be bothered, would require a lot of cutting and just a PIA for maintenance as you’ve already expressed.
ngl Idk if I would of went this route either if the 180 gal display tank and the 55 gal tank I used for the sump weren't free LOL.

I chipped my glass sump on my old 125 and didn't want to go through that trauma again
 
1~1.1 ph drop on my 180gal tank /60 gallon sump with a yugang reactor. my sump is mostly sealed and so is the back of my overflow box

183 days so far. Im down to 500 psi on the 20lb so far
74.6% of My surface area is covered

It's garbage for scaping/maintenance work but I wont deny that it helps save a lot of co2

I've been experimenting with a lid ( on my open topped tank) that I could close nearly perfectly.

For anyone who is interested to explore, I used water evaporation as an indicator for the gas exchange. So if I would have 15 mm evaporation with open tank, reduced to just a few mm with a closed lid I could reasonable estimate that gas exchange had been reduced with 90%. I have never seen any impact on the tank's health when limiting gas exchange by 90%, but it does pay back in very substantial savings on CO2.

My guess would be that @SingAlongWithTsing can aim for a once-a-year CO2 tank refill by just closing some if his access holes when they are not needed.

Here is my lid. The strips are for mechanical stability and supporting the weight, and for a more tight fit to the tank.

1708740222392.png
 
Last edited:
I did collect some data on another forum
Thanks @Zeus. for posting this table. Obviously there is a huge range of days that one tank lasts. And as you say, there are many factors that affect CO2 used, so let me give my perspective on how we may try and predict consumption.

From the table I see a bunch around 0.015 grams/litre, and then it ranges upto about 4 times higher, 0.06. So if anything could be taken from these data, what would it be? Probably that tank volume is no good predictor.

From the physics perspective, Ficks law, the tanks outgassing is a function of CO2 concentration difference and surface area between water and ambient air. Although there may be a weaker correlation, having the tank's volume as independent variable is not the best choice, nor is grams/litre a usefull variable to model consumption. The key should be tank surface area, CO2 ppm and how many hours used per day.

surface agitation level
The agitation is not really a factor, as long as the water is not stagnant and as long as the water does not have a 'dirty" surface layer that would limit outgassing. It is really the surface area that counts.

So in summary, when we have a clean and non stagnant water surface we can predict CO2 consumption almost exclusively from surface area, CO2 ppm and injection time. All other parameters, although relevant, are of lesser importance.
 
Last edited:
From the physics perspective, Ficks law, the tanks outgassing is a function of CO2 concentration difference and surface area between water and ambient air. Although there may be a weaker correlation, having the tank's volume as independent variable is not the best choice, nor is grams/litre a usefull variable to model consumption. The key should be tank surface area, CO2 ppm and how many hours used per day.
And Hindsight is the best foresight esp. in collecting Data, once collected the original data parameters reviewed different parameters would be reconsidered from those results. But we work with what we have to hand. I was also after DC colour but found that hard for users to supply
So in summary, when we have a clean and non stagnant water surface we can predict CO2 consumption almost exclusively from surface area, CO2 ppm and injection time. All other parameters, volume or agitation, are of lesser importance.

A would say agitation is also a big factor also as CO2 /O2 is so -so slow to diffuse in water, after all a fish must use active means to exchange gases in non flowing water but in current non active methods can be used
 
And Hindsight is the best foresight esp. in collecting Data, once collected the original data parameters reviewed different parameters would be reconsidered from those results. But we work with what we have to hand. I was also after DC colour but found that hard for users to supply
The problem in the thread on the other forum is that data analysis is done from an incorrect understanding of the physics involved. Gram CO2 per litre water is never going to give reliable conclusions, it is only gram per tank surface area that will see a reliable correlation over several tanks. And as you say you would need to have an concentration estimation from drop checker of pH drop as well.

In another thread I proposed cooperation with a manufacturer to measure some basic physics parameters and use these for further dynamic calculations of CO2 (like the mentioned CO2 consumption), but no replies as of yet
I have not done the measurements, but am pretty confident that CO2 consumption can be predicted with probably 5-10% accuracy, when the parameters are known.

A would say agitation is also a big factor also as CO2 /O2 is so -so slow to diffuse in water
For no-nonsense, and less experienced hobbyists it indeed makes sense to emphasise good surface agitation. So what I am saying here is for anyone who likes to dive a bit deeper into the science, or would be interested to make predictive models of CO2 consumption.

The diffusion of CO2 in water is indeed slow, and this would be a dominant issue if transport would be mainly by diffusion as it is in stagnant water or stagnant surface layers (water, oil, or similar). But when the water surface is clean (either by skimmer, overflow or sufficient agitation) AND the water and water surface have sufficient flow (not stagnant), transport of CO2 will not be mainly by diffusion (on a microscopic level) but rather by CO2 being transported by the water flow (macroscopic). In this case, unless the water surface is dirty or stagnant, the outgassing will be proportional to surface area and concentrations, but to a much lesser extent (if any) by agitation.

So in summary, it is a good advice to have decent surface agitation but at the same time it is a misunderstanding that CO2 consumption would continue to increase with increased surface agitation above a certain minimum level.
 
The agitation is not really a factor, as long as the water is not stagnant and as long as the water does not have a 'dirty" surface layer that would limit outgassing. It is really the surface area that counts.
Doesn't agitation greatly increase the surface area though?
 
Doesn't agitation greatly increase the surface area though?
Yes, waves will create a larger surface area than just a flat surface. But you need big waves, for the difference to be significant or even great. What really counts is flow, everywhere in the tank, so as to avoid stagnant and diffusion limited boundary layers.

The common mistake is to reduce surface agitation in an attempt to limit CO2 consumption, so from that perspective it is always good to recommend good flow and surface agitation, as this will enhance gaseous exchange as well as CO2 stabilisation.
 
Last edited:
I've been experimenting with a lid ( on my open topped tank) that I could close nearly perfectly.
I am currently doing some further experimentation, as I want to prepare my tank for a long absence without anyone taking care for a month or two.

I can't say I understand all aspects well enough, but with my lid almost entirely closing the tank and perhaps 75% reduced CO2 consumption my tank is doing great. I inject very little, but start really early in the morning to provide still good stability. Fish are fine, and even the Wallichi that is usually picky on CO2 stability does not stunt. Drop checker looks good.

The take away is that whether a tank is covered or not can make a huge (I would say up to 80%) difference on CO2 consumption. Any comparison between covered and non covered tanks seems almost meaningless to me.
 
So late to the party here and I feel dumb posting this after the technical discussion that has been happening on this thread (fascinating by the way).

I use a 5 lb cylinder as it must fit inside my cabinet. It lasts me about a month and a half to two months. I usually let it run empty due to laziness. However, I will be getting a new 5 lb cylinder that I will keep filled and do a swap like I used to do.

The closed lid discussion above is interesting to me. I've never done this because I think the condensation will cause the lid to become cloudy and start to limit light penetration. Also, not sure how I would feed the fish as I use an auto-feeder.
 
The closed lid discussion above is interesting to me. I've never done this because I think the condensation will cause the lid to become cloudy and start to limit light penetration.
I use a closed lid on my 500L it was a PITA, had to remove glass and clean it, and yes it will affect the PAR levels IMO, Plus a braced tank is higher than an open top tank so needed small pair of step ladders to reach the substrate level in center of tank as 50cm deep to substrate.
 
The closed lid discussion above is interesting to me. I've never done this because I think the condensation will cause the lid to become cloudy and start to limit light penetration. Also, not sure how I would feed the fish as I use an auto-feeder.
I have an open tank, and for the periods that I am experimenting I close it. The lighting unit is on top of the acrylic, and the heat from the LED's keeps that part of the acrylic free from water condensation. A one inch hole for feeding.

I use a closed lid on my 500L it was a PITA
I would agree, and what I do is just for experiments and as a solution when I am away from home for a month or two.

If and when I buy my next tank, it will definitely be closed with the light unit inside. No need for a lid then. This will be much easier to control CO2, as well as save probably up to 80-90% on CO2 consumption.

So, going back to the question from the OP - the main factors that mainly influence the lifetime of the CO2 bottle are:
  • CO2 ppm in the tank (some may target 10 ppm, others 40 so that would be a factor of 4 difference)
  • Tank surface area, including sump surface area (rather than volume)
  • Whether tank and sump are covered or an open system with direct gas exchange to ambient air (this may be a huge variation as well)
 
Last edited:
Back
Top