method to measure CO2 degas of tap water for WC in low tech

a1Matt

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I have filled two 25l water containers with tap water, added dechlor, screwed the lids back on them and am letting them sit until any CO2 from the tap has degassed.

In order to check that the CO2 level has reached equilibrium with the air I am going to measure the ph level and when it stops changing (rising?) then I deduce that equilibrium will have been reached.

Is this logic sound?
Do I need to leave the caps off of the water containers?
Anything else I have missed?


The driving force behind all this is that I want to make some water changes on my non CO2 tank as I have had some shrimp deaths and I think there is an ammonia spike\some toxicity in the water that water changes will help to remove.

As the tank is non CO2 if I carry out the water change with fresh tap water I will induce an outbreak of BBA in the tank due to the change in CO2 levels. I appreciate that water with CO2 at equilibrium with the air will not be an exact match of my tanks CO2 but I figure it will be as close as I can achieve.

I know this is clearly water chemistry related, but as it is pertinent for a low tech tank I have posted it in the low tech forum. I don't mind if it gets moved to water chemistry!
 

GreenNeedle

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Just degassing it for 24 hours should be fine. Put an airstone in it to make it quicker.

AC
 

a1Matt

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I guess that 24 to 48 hours would be best, but it would be nice though to be able to confirm for myself how long it takes to degas with my method, especially as I have a PH meter to hand.
 

Brenmuk

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I think it will be a challenge to measure the CO2 in your containers and I'm not sure it would be worth it anyway.
What makes you think that tap water is not already in equilibrium with air?

Correct me if I wrong but I though fluctuating CO2 levels has more to do with how your tank is run rather than water changes ie plants use up CO2 during lights on period and it builds up when lights off - more plants more CO2 demand & ph/buffering etc.
Just letting tap water sit in a container overnight where it can heat up to room temp will degass it a bit as water holds less disolved gas with increasing temp.

As for the shrimps if you suspect water quality is a problem then you could add water conditioners to the new water you are adding to the tank. You may also wish to use alternatives to tap water such as R.O. or rain water.

You may also be interested in a thread that Diana Walstead has started where she has set up mini NPTs for cherry shrimps using old tank water from her other NPT's. The rationale behind this is that she believes that aged water from a NPT will be rich is natuarally occurring chelators that would bind to any heavy metals - see http://www.aquaticplantcentral.com/forumapc/el-natural/62825-new-npt-shrimp-tanks.html.
Theres also another link there on CO2 degassing http://www.aquaticplantcentral.com/forumapc/el-natural/63138-water-movement-co2-degassing.html.
 

a1Matt

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Thanks for your input. I will explain my perspective a little more. Should be a good discussion :) Remember this is an exercise in curiosity for me and not a big deal :) At the end of the day I amlooking for a bit more understanding and if I can make a slight tweak to how I do things that keeps the dreaded BBA from popping its ugly head then that is a bonus.

Brenmuk said:
I think it will be a challenge to measure the CO2 in your containers and I'm not sure it would be worth it anyway.

I agree it will be a challenge to measure the 'actual' CO2. I just want to know when it hits equilibrium.

Here is my logic...
CO2 can be measured by taking PH and KH values then referencing that against the ubiqitous PH\KH table.
The KH is not going to change by the degassing process, so that is a constant and can be ignored. Therefore when the ph stops changing it is at equilibrium (whatever that is).
If the ph never changes, then it was at equilibrium to start with :rolleyes:

Does it take 24 hours to get there? or maybe only 12?
How much does aerating speed this up?
I have no idea at all - that is why I want to experiment with this.
It is a quick test - after all, all I am doing is sticking in a ph meter.
My agenda from this thread is... is my logic in using the ph to test when CO2 has reached equilibrium sound?


Brenmuk said:
What makes you think that tap water is not already in equilibrium with air?

From reading here and on Barr report. I could well be wrong. Amongst others, I saw a post by Tom Barr once that said the reasons why tap water is sometimes (not always) higher in CO2. Frustratingly I do not know any details. Another reason to play with it myself ;)


Brenmuk said:
Correct me if I wrong but I though fluctuating CO2 levels has more to do with how your tank is run rather than water changes ie plants use up CO2 during lights on period and it builds up when lights off - more plants more CO2 demand & ph/buffering etc.

I see what you mean, and I agree...
To do a through test I need to know the CO2 levels in the tank, how else could I compare them to the tap water?
But, I would not even try to get an accurate CO2 reading of my tank water, as there are too many variables. (i.e. other things that affect the ph and kh).
So in this thread I am only interested in how loaded the tap water is with CO2.

Switching from experiment logic and back to practialities, I will do my water change when the tank itself is as close to equilibrium as possible.
I deduce this is just before lights on, as I figure the main input on CO2 levels is the plants using it up, and at this time the plants will be 'resting'.

Brenmuk said:
Just letting tap water sit in a container overnight where it can heat up to room temp will degass it a bit as water holds less disolved gas with increasing temp.

I hadn't thought about temp. I will have to make some compensation for temp changes in my readings

Brenmuk said:
As for the shrimps if you suspect water quality is a problem then you could add water conditioners to the new water you are adding to the tank. You may also wish to use alternatives to tap water such as R.O. or rain water.

Yes! I always add dedchlor\conditioner to tap water. I also only usually do top ups, and for this I use RO. I am frugal though, and do not want to spend money on RO for large water changes.

Brenmuk said:
You may also be interested in a thread that Diana Walstead has started where she has set up mini NPTs for cherry shrimps using old tank water from her other NPT's. The rationale behind this is that she believes that aged water from a NPT will be rich is natuarally occurring chelators that would bind to any heavy metals - see http://www.aquaticplantcentral.com/forumapc/el-natural/62825-new-npt-shrimp-tanks.html.
Theres also another link there on CO2 degassing http://www.aquaticplantcentral.com/forumapc/el-natural/63138-water-movement-co2-degassing.html.

Very interested in this indeed. I will study these links. Thanks.
 

aaronnorth

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In order to check that the CO2 level has reached equilibrium with the air I am going to measure the ph level and when it stops changing (rising?) then I deduce that equilibrium will have been reached.

Is this logic sound?
Do I need to leave the caps off of the water containers?
Anything else I have missed?

leaving the caps off or on will play a role in the equilbrium. If you leave it on, then the air space will be smaller in volume, therefore it will be a higher concentration of CO2, as apposed it gassing off CO2 in the whole room for it to diffuse into ;) (diffuse = high concentration going into a lower concentration). so the equilibrium with CO2 - air will be higher. you will just have to try and replicate the aquarium conditions, and as above, temperature will have a big affect

aerating increases the surface area of the water's surface, therefore increasing the speed of gaseous exchange, i am not sure how you calculate this, there may be a way, but it will be more than likely too confusing! (no offense)

I found this:
The number of 20 or so PPM of C02 sticks in my mind as what I've seen
> thrown around as target level for a planted tank. What is this
> concentration as expressed relative to the ratio of air in the tank. Or to
> say in another way, what is atmospheric concentration of C02 that would
> produce a 20 ppm level in water in a system in equilibrium, assuming no
> production or consumption of CO2.

CO2 is only about 0.03% of "normal" dry air, and water in balance with
air will contain only about 0.42 mg/l of CO2 at 25C (about 77F). That
number drops noticably as temperatures increase. A concentration of 20
ppm CO2 is 48 times the atmospheric balance point; it's what the water
would balance at if the air contained about 1.4% CO2.

In an established aquarium without much photosynthesis going on, I think
CO2 concentrations are typically 3-4 ppm - higher than the concentration
that would balance with the atmosphere. The value is higher because of
CO2 from respiration in the tank.

you might be able to work something out from it.
thanks.
 

a1Matt

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aaronnorth said:
leaving the caps off or on will play a role in the equilbrium. If you leave it on, then the air space will be smaller in volume, therefore it will be a higher concentration of CO2, as apposed it gassing off CO2 in the whole room for it to diffuse into ;) (diffuse = high concentration going into a lower concentration). so the equilibrium with CO2 - air will be higher.

I vaguely suspected this, thanks for confirming!

aaronnorth said:
you will just have to try and replicate the aquarium conditions, and as above, temperature will have a big affect

I did forget about temp initially :oops: , so you and Brenmuk have helped me out with this info 8)

aaronnorth said:
aerating increases the surface area of the water's surface, therefore increasing the speed of gaseous exchange, i am not sure how you calculate this, there may be a way, but it will be more than likely too confusing! (no offense)

No offense taken :D I figured I 'could' repeat the test a couple of times, once with aeration and once without. Not even vaguely scientific, and undoubtedly not overly accurate either. But! as I don't have an airpump it is a fairly moot point anyway. lol.

aaronnorth said:
I found this:
The number of 20 or so PPM of C02 sticks in my mind as what I've seen
> thrown around as target level for a planted tank. What is this
> concentration as expressed relative to the ratio of air in the tank. Or to
> say in another way, what is atmospheric concentration of C02 that would
> produce a 20 ppm level in water in a system in equilibrium, assuming no
> production or consumption of CO2.

CO2 is only about 0.03% of "normal" dry air, and water in balance with
air will contain only about 0.42 mg/l of CO2 at 25C (about 77F). That
number drops noticably as temperatures increase. A concentration of 20
ppm CO2 is 48 times the atmospheric balance point; it's what the water
would balance at if the air contained about 1.4% CO2.

In an established aquarium without much photosynthesis going on, I think
CO2 concentrations are typically 3-4 ppm - higher than the concentration
that would balance with the atmosphere. The value is higher because of
CO2 from respiration in the tank.

you might be able to work something out from it.
thanks.
[/quote]

Cheers. So they are saying that 'standing water' is 4.2ppm @ 25deg C. and a tank with no photosynthesis is typically 3-4ppm. That is why I am going for a 'lights out' water change. So that I cna get as close to this 3/4ppm as possible. I am aware that as well as photosynthesis, surface movement in the tank will also have an effect on the tanks CO2 level. I figure that is too hard to measure, so I am ignoring it!
 

ceg4048

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a1Matt said:
I guess that 24 to 48 hours would be best, but it would be nice though to be able to confirm for myself how long it takes to degas with my method, especially as I have a PH meter to hand.
Equilibrium is reached after a couple hours but the lid must be off.

Cheers,
 

aaronnorth

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a1Matt said:
aaronnorth said:
leaving the caps off or on will play a role in the equilbrium. If you leave it on, then the air space will be smaller in volume, therefore it will be a higher concentration of CO2, as apposed it gassing off CO2 in the whole room for it to diffuse into ;) (diffuse = high concentration going into a lower concentration). so the equilibrium with CO2 - air will be higher.

I vaguely suspected this, thanks for confirming!

aaronnorth said:
you will just have to try and replicate the aquarium conditions, and as above, temperature will have a big affect

I did forget about temp initially :oops: , so you and Brenmuk have helped me out with this info 8)

aaronnorth said:
aerating increases the surface area of the water's surface, therefore increasing the speed of gaseous exchange, i am not sure how you calculate this, there may be a way, but it will be more than likely too confusing! (no offense)

No offense taken :D I figured I 'could' repeat the test a couple of times, once with aeration and once without. Not even vaguely scientific, and undoubtedly not overly accurate either. But! as I don't have an airpump it is a fairly moot point anyway. lol.

aaronnorth said:
I found this:
The number of 20 or so PPM of C02 sticks in my mind as what I've seen
> thrown around as target level for a planted tank. What is this
> concentration as expressed relative to the ratio of air in the tank. Or to
> say in another way, what is atmospheric concentration of C02 that would
> produce a 20 ppm level in water in a system in equilibrium, assuming no
> production or consumption of CO2.

CO2 is only about 0.03% of "normal" dry air, and water in balance with
air will contain only about 0.42 mg/l of CO2 at 25C (about 77F). That
number drops noticably as temperatures increase. A concentration of 20
ppm CO2 is 48 times the atmospheric balance point; it's what the water
would balance at if the air contained about 1.4% CO2.

In an established aquarium without much photosynthesis going on, I think
CO2 concentrations are typically 3-4 ppm - higher than the concentration
that would balance with the atmosphere. The value is higher because of
CO2 from respiration in the tank.

you might be able to work something out from it.
thanks.

Cheers. So they are saying that 'standing water' is 4.2ppm @ 25deg C. and a tank with no photosynthesis is typically 3-4ppm. That is why I am going for a 'lights out' water change. So that I cna get as close to this 3/4ppm as possible. I am aware that as well as photosynthesis, surface movement in the tank will also have an effect on the tanks CO2 level. I figure that is too hard to measure, so I am ignoring it![/quote]

when you say "lights out water change" is that for this experiment? there is still other microorganisms respiring in the water, albeit there wont be as many as your aquarium.
 

a1Matt

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ceg4048 said:
a1Matt said:
I guess that 24 to 48 hours would be best, but it would be nice though to be able to confirm for myself how long it takes to degas with my method, especially as I have a PH meter to hand.
Equilibrium is reached after a couple hours but the lid must be off.

Cheers,

Wow! A couple of hours, that is a lot quicker than I thought. (and the lids are coming off ASAP.)

Do you think my proposal that we can tell when the degassing is complete by the PH value stabilising is valid?


aaronnorth said:
when you say "lights out water change" is that for this experiment? there is still other microorganisms respiring in the water, albeit there wont be as many as your aquarium.

oops, I was not very clear on this.
What I meant by "lights out water change" is that once I have my prepared degassed tap water I will then put in in the tank at a time when the tank has the lights off.

For the experiment I would just measure PH and temp at regular intervals starting from when I fill the containers and ending when the PH no longer changes. Ignoring light\microrganisms completely.
 

ceg4048

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a1Matt said:
ceg4048 said:
a1Matt said:
I guess that 24 to 48 hours would be best, but it would be nice though to be able to confirm for myself how long it takes to degas with my method, especially as I have a PH meter to hand.
Equilibrium is reached after a couple hours but the lid must be off.

Cheers,

Wow! A couple of hours, that is a lot quicker than I thought. (and the lids are coming off ASAP.)

Do you think my proposal that we can tell when the degassing is complete by the PH value stabilising is valid?
Yes this is valid but also remember that equilibrium is not a static thing. Degassing is just a matter of having the higher CO2 content in the water escape, but afterward, CO2 will also dissolve into water from atmosphere and will also move out across the water/air interface depending on temperature changes and barometric pressure, so there may be minor pH variations even after a few hours. As Supercoley1 says, use an airstone and it will be very quick. How long does it take for a glass of Cola to go flat sitting on the counter? What happens when you shake it up? CO2 moves very easily into and out of solution. 8)

Cheers,
 

GreenNeedle

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Brenmuk said:
What makes you think that tap water is not already in equilibrium with air?

Correct me if I wrong but I though fluctuating CO2 levels has more to do with how your tank is run rather than water changes ie plants use up CO2 during lights on period and it builds up when lights off - more plants more CO2 demand & ph/buffering etc.
Just letting tap water sit in a container overnight where it can heat up to room temp will degass it a bit as water holds less disolved gas with increasing temp.

Nope tap water contains much higher levels of CO2 under pressure. With non CO2 tanks that means the water is at equilibrium and then do a water change straight from the tap and you increase CO2. Means things are unstable.

Water turbulence on a non CO2 tank is a good thing because it will allow the natural equilibrium to be replenished much quicker. The plants will use CO2 and returning to equilibrium takes time so the water turbulence means it will happen much faster.

AC
 

a1Matt

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Cheers Clive. That was spot on the info I was after, with a nice analogy in clear lay terms chucked in as well :) :thumbs up smiley: :D Now I just need that new battery for the PH meter and a glass of coke :lol: .....
 

a1Matt

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SuperColey1 said:
Brenmuk said:
What makes you think that tap water is not already in equilibrium with air?

Correct me if I wrong but I though fluctuating CO2 levels has more to do with how your tank is run rather than water changes ie plants use up CO2 during lights on period and it builds up when lights off - more plants more CO2 demand & ph/buffering etc.
Just letting tap water sit in a container overnight where it can heat up to room temp will degass it a bit as water holds less disolved gas with increasing temp.

Nope tap water contains much higher levels of CO2 under pressure. With non CO2 tanks that means the water is at equilibrium and then do a water change straight from the tap and you increase CO2. Means things are unstable.

Water turbulence on a non CO2 tank is a good thing because it will allow the natural equilibrium to be replenished much quicker. The plants will use CO2 and returning to equilibrium takes time so the water turbulence means it will happen much faster.

AC

The points you make here Andy are the assumptions I was working off of. Although I did not realise why the tap water is higher in CO2 - thanks for explaining that it due to the higher pressure.
 

GreenNeedle

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Not overly sure if it is due to the pressure!!! Just know that tap water is higher :)

AC
 

ceg4048

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The level of CO2 concentration in water is determined by where the water comes from and what natural components it interfaces with on it travels towards your tap. Additionally, the solubility of gases in fluid mixtures is highly dependent on the fluids temperature. William Henry (an English chemist no less) figured this out out in the early 19th century. The principle has become known as Henry's Law. So if you turn the tap on full cold, then that water will have more dissolved CO2 than the water coming from your water heater. In winter, the overall dissolved levels will be higher than in summer. You can even buy bottled (so-called) mineral water with exotic French names at Tesco that has come into contact with CO2 sources via (supposedly) mountain springs. I think they actually charge you more for that gas content (surprisingly :wideyed: ). They call it "Sparkling" water versus lower CO2 content "Still" water.

Cheers,
 

Brenmuk

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SuperColey1 said:
Brenmuk said:
What makes you think that tap water is not already in equilibrium with air?

Correct me if I wrong but I though fluctuating CO2 levels has more to do with how your tank is run rather than water changes ie plants use up CO2 during lights on period and it builds up when lights off - more plants more CO2 demand & ph/buffering etc.
Just letting tap water sit in a container overnight where it can heat up to room temp will degass it a bit as water holds less disolved gas with increasing temp.

Nope tap water contains much higher levels of CO2 under pressure. With non CO2 tanks that means the water is at equilibrium and then do a water change straight from the tap and you increase CO2. Means things are unstable.

Water turbulence on a non CO2 tank is a good thing because it will allow the natural equilibrium to be replenished much quicker. The plants will use CO2 and returning to equilibrium takes time so the water turbulence means it will happen much faster.

AC

Fair enough - tap water that has been under pressure and is cooler than your tank water is going to contain higher levels of CO2. I suppose the point I had in my mind that I didn't make very clear is that if you run a low tech tank and do infrequent water changes (I do 50% every 6 months) then fluctuating CO2 levels caused by water changes is not that significant compared to other aspects of tank maintenance - If on the other hand you do 50% weekly...

By water turbulence do you mean surface turbulence that you get by running an air stone for example?
There seems to be a number of people who run low tech/el naturel tanks who believe that while water circulation is good you should avoid excessive water surface turbulence to try to preserve the extra CO2 that occurs in tanks (ie from soil, fish/bacterial respiration etc). I have also read good counter arguments that say that CO2 will be depleted soon after lights on in a well planted tank and that running an air stone an hour or so into the lights on period would help raise tank CO2 levels back to atmospheric levels.
Interestingly during my last water change I cleaned out my external filter which had blocked and had for some time produced little or no water circulation - the plants and fish seemed as healthy as ever.
 

GreenNeedle

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I run a decent amount and have no problems although my non CO2 tank is only a month and a half old. It is however very small, open toped and gets top ups straight from the tap every couple of days.

A lot of people tell us that equilibrium is 0.5ppm but as I understand it that is in sterile water. I would think in non sterile water the between 3 and 8ppm is much more likely. Even dust/particles decompose and produce CO2!!!

AC
 

a1Matt

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Brenmuk said:
Fair enough - tap water that has been under pressure and is cooler than your tank water is going to contain higher levels of CO2. I suppose the point I had in my mind that I didn't make very clear is that if you run a low tech tank and do infrequent water changes (I do 50% every 6 months) then fluctuating CO2 levels caused by water changes is not that significant compared to other aspects of tank maintenance - If on the other hand you do 50% weekly...

I missed your point before. In my tank even just topping up with tap is likely to cause a mild increase in the growth of BBA across my substrate. Thing is though, I had rampant BBA issues before I switched to low tech. From your experience it sounds like once I have the BBA nailed, then topping up\periodic water changes won't be much of an issue. I might use Excel to completely eradicate the BBA then go back to low tech again.

Brenmuk said:
By water turbulence do you mean surface turbulence that you get by running an air stone for example?
There seems to be a number of people who run low tech/el naturel tanks who believe that while water circulation is good you should avoid excessive water surface turbulence to try to preserve the extra CO2 that occurs in tanks (ie from soil, fish/bacterial respiration etc). I have also read good counter arguments that say that CO2 will be depleted soon after lights on in a well planted tank and that running an air stone an hour or so into the lights on period would help raise tank CO2 levels back to atmospheric levels.
Interestingly during my last water change I cleaned out my external filter which had blocked and had for some time produced little or no water circulation - the plants and fish seemed as healthy as ever.

I have (through neglect, rather than intentionally) had very low circulation for months, with no problems. Then I recently increased my plant mass and things went really wrong with my shrimp shortly after. I suspect low flow was a contributing factor to my problems.

I am not inclined to believe that my substrate\fish\bacteria are producing any siginifcant amount of CO2. The counter arguments recommending higher turbulence seem more sensible to me (so that is what I am aiming for now, via a spraybar angled at the surface). At the end of the day I can not keep up with the science behind either argument so I will try both ways and see the difference for myself.
 

Brenmuk

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It will be interesting to see how you get on with your spraybar. I have my tank in the living room so I prefer to avoid using spraybars and airstones because of the noise - the sound of continuous running water makes me need the loo all the time! :bored:
 
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