Ptarmigan
Fish Fanatic
.
Co2, No Need To Measure Kh
- Thread starter Ptarmigan
- Start date
jmuccillo
Fish Fanatic
All sounds very logical.
If you're mathematically inclined here's an explanation for it.
A simple formula for relating CO2 to pH and KH is:
CO2 = 3xKHx10^(7-pH)
where CO2 in ppm and kH in degrees.
Taking logs of both sides and after a bit of algebra you get:
pH = 7-log(CO2/3KH)
If you now consider a pH swing pH(2) - pH(1) and assume KH is constant then after a bit more algebra you find KH drops out and you're left with
pH Swing = pH(2)-pH(1) = -log(CO2(2)/CO2(1))
So if your CO2 starts at 3ppm and increases to 30ppm then the pH swing is equal to -log(30/3) = -1.
Ie pH reduces by 1 regardless of kH.
Hope this isn't too confusing.
If you're mathematically inclined here's an explanation for it.
A simple formula for relating CO2 to pH and KH is:
CO2 = 3xKHx10^(7-pH)
where CO2 in ppm and kH in degrees.
Taking logs of both sides and after a bit of algebra you get:
pH = 7-log(CO2/3KH)
If you now consider a pH swing pH(2) - pH(1) and assume KH is constant then after a bit more algebra you find KH drops out and you're left with
pH Swing = pH(2)-pH(1) = -log(CO2(2)/CO2(1))
So if your CO2 starts at 3ppm and increases to 30ppm then the pH swing is equal to -log(30/3) = -1.
Ie pH reduces by 1 regardless of kH.
Hope this isn't too confusing.
I understand the logic of this PtarmiganUK and you appear to have a valid point.
However, your calculations assume a steady pH/KH level of tap water. Unfortunately this isn't the case for a lot of people. KH/pH levels can vary through the year. Some people can have sudden massive swings in KH/pH.
If you do a water change and your tap water KH/pH has suddenly changed this would make a mess of your calculations.
I would always advise the regular use of KH and pH test kits when injecting CO2.
HTH.
However, your calculations assume a steady pH/KH level of tap water. Unfortunately this isn't the case for a lot of people. KH/pH levels can vary through the year. Some people can have sudden massive swings in KH/pH.
If you do a water change and your tap water KH/pH has suddenly changed this would make a mess of your calculations.
I would always advise the regular use of KH and pH test kits when injecting CO2.
HTH.
Ptarmigan
Fish Fanatic
.
I used to be, but it is a long time since I practised that bit of brain celljoe2 said:
Thanks, excellent explanation . (so Im not quite as mad as I thought I was after all !!)
yay for plastic plants.. well.. at least not fully planted eh...
Ptarmigan
Fish Fanatic
.
You've obviously put a lot of thought in to this and I think it's an interesting topic.
Taking a jar of tank water and letting it sit until it reaches equilibrium (24hrs?) is a good idea. But, would the baseline measure in the open top jar, be the same as the water in a tank with a hood on that contains fish?
Also your original assumption is of a tank with a CO2 level of 3 mg/l. That's a pretty good guess and most tanks would probably fall somewhere near that mark. However, as you know this can vary depending on how well a room is ventilated, whether the tank has a hood or not, fish load etc.
A tank without a hood, with a low fish load, in a well ventilated room, may have a pH of 7.6. Another tank with a hood, high fish load, in a not so well ventilated room may also have a pH of 7.6. Although both tanks have the same pH level, their baseline CO2 levels may be totally different. One could have a KH of 2.5, while the other could have a KH of 5.
This could make the inital assumption of an equilibrium level of 3 mg/l inaccurate and ruin any future calculations.
I don't mean to nitpick. I know you are not advocating using this method and I take my hat off to you for raising such a question. I just don't think it could work with any level of accuracy.
Taking a jar of tank water and letting it sit until it reaches equilibrium (24hrs?) is a good idea. But, would the baseline measure in the open top jar, be the same as the water in a tank with a hood on that contains fish?
Also your original assumption is of a tank with a CO2 level of 3 mg/l. That's a pretty good guess and most tanks would probably fall somewhere near that mark. However, as you know this can vary depending on how well a room is ventilated, whether the tank has a hood or not, fish load etc.
A tank without a hood, with a low fish load, in a well ventilated room, may have a pH of 7.6. Another tank with a hood, high fish load, in a not so well ventilated room may also have a pH of 7.6. Although both tanks have the same pH level, their baseline CO2 levels may be totally different. One could have a KH of 2.5, while the other could have a KH of 5.
This could make the inital assumption of an equilibrium level of 3 mg/l inaccurate and ruin any future calculations.
I don't mean to nitpick. I know you are not advocating using this method and I take my hat off to you for raising such a question. I just don't think it could work with any level of accuracy.
Ami
Fishaholic
Wow PtarmiganUK! That sounded like an excellent suggestion - then maths (algebra!) got involved and then Iggy started 'nitpicking' ....
I think that this could work for each individual in their own tanks. I know that my tank has a glass cover and hood, plus the filter is mid tank (little surface disturbance - none at the mo cos it's broke!), my water is hard (generally around 8.5), I have a sand substrate and not too heavily planted.
If I could have a rough idea of the CO2 level before nutrafin (probably around 2mg/l) and what my pH was (8.5), then presumably I could use (simple please!) maths to keep track of it - including water changes if I test both my tap water and tank water and make an adjustment.
However, I'm no mathmatician (can't even spell it!) so I'm not sure it would work for me.
Perhaps Joe could invent some sort of calculator for us to give an estimate?
Ami
....I think that this could work for each individual in their own tanks. I know that my tank has a glass cover and hood, plus the filter is mid tank (little surface disturbance - none at the mo cos it's broke!), my water is hard (generally around 8.5), I have a sand substrate and not too heavily planted.
If I could have a rough idea of the CO2 level before nutrafin (probably around 2mg/l) and what my pH was (8.5), then presumably I could use (simple please!) maths to keep track of it - including water changes if I test both my tap water and tank water and make an adjustment.
However, I'm no mathmatician (can't even spell it!) so I'm not sure it would work for me.
Perhaps Joe could invent some sort of calculator for us to give an estimate?
Ami
Ptarmigan
Fish Fanatic
.
Ami
Fishaholic
Ptarmigan
Fish Fanatic
.
jmuccillo
Fish Fanatic
I'd love to be able to write a calculator for you but unfortunately my computer programming skills are not on par with my algebra skills. Perhaps someone who is more computer literate than me could take it on board. Fortunately, the CO2 charts are pretty easy to use so you could probably get by just using them.
Perhaps someone who is more computer literate than me could take it on board. Fortunately, the CO2 charts are pretty easy to use so you could probably get by just using them.Ptarmigan
Fish Fanatic
.
Wow PtarmiganUK! You're like a dog with a bone......you don't let go.
Seriously though, I think you raise some excellent points.
I couldn't disagree with your point about test kits. They aren't always accurate, although it is my understanding that KH kits are generally amongst the most accurate that we use. Most ask you to fill a test vial with 5 ml of water and each drop of liquid represents 1 dKH until there's a change of colour. Accuracy can of course be increased by filling the vial with 10 ml of water and counting the drops. Each drop then represents 0.5 dKH. As for pH kits, I believe most are accurate to within +/- 0.2 .
As for the jar theory, I honestly don't know whether the water would settle to the same equilibrium as the tank. That's why I put a ? there.
I do think though, that finding the equilibrium level of a tank without a KH test kit would be very difficult. Surely finding the equilibrium level would be the crucial point of this theory. As I stated earlier, with the two examples of tanks I gave, I believe it's possible for two tanks to have the same pH levels and differing KH's.
IE
tank No1 has a pH of 7.6, but because it has no hood and a low fish load and is in a room which is well ventilated ( CO2 levels outside are said to be 0.3 mg/l ). It has an equilibrium level of 1.9 mg/l CO2.
Tank No2 also has a pH of 7.6, a tight fitting hood and a high fish load, with very little outside air coming into the room. It has an equilibrium level of 3.8 mg/l.
If you were to drop the pH of tank No1 by 1.0 it would only have a CO2 level of 18.8 mg/l. If you dropped the pH of tank No2 by the same amount the CO2 level would be 37.7 mg/l . That's quite a difference in CO2 levels.
I still think you have raised a very interesting topic and I don't think I have seen this discussed before. Hopefully some of the other more experienced members of the forum could give us some input.
Seriously though, I think you raise some excellent points.
I couldn't disagree with your point about test kits. They aren't always accurate, although it is my understanding that KH kits are generally amongst the most accurate that we use. Most ask you to fill a test vial with 5 ml of water and each drop of liquid represents 1 dKH until there's a change of colour. Accuracy can of course be increased by filling the vial with 10 ml of water and counting the drops. Each drop then represents 0.5 dKH. As for pH kits, I believe most are accurate to within +/- 0.2 .
As for the jar theory, I honestly don't know whether the water would settle to the same equilibrium as the tank. That's why I put a ? there.
I do think though, that finding the equilibrium level of a tank without a KH test kit would be very difficult. Surely finding the equilibrium level would be the crucial point of this theory. As I stated earlier, with the two examples of tanks I gave, I believe it's possible for two tanks to have the same pH levels and differing KH's.
IE
tank No1 has a pH of 7.6, but because it has no hood and a low fish load and is in a room which is well ventilated ( CO2 levels outside are said to be 0.3 mg/l ). It has an equilibrium level of 1.9 mg/l CO2.Tank No2 also has a pH of 7.6, a tight fitting hood and a high fish load, with very little outside air coming into the room. It has an equilibrium level of 3.8 mg/l.
If you were to drop the pH of tank No1 by 1.0 it would only have a CO2 level of 18.8 mg/l. If you dropped the pH of tank No2 by the same amount the CO2 level would be 37.7 mg/l . That's quite a difference in CO2 levels.
I still think you have raised a very interesting topic and I don't think I have seen this discussed before. Hopefully some of the other more experienced members of the forum could give us some input.
Ptarmigan
Fish Fanatic
.
Similar threads
Most reactions
-
351 -
224 -
223 -
192
-
188 -
184 -
160 -
153 -
142 -
139 -
134
-
132 -
109 -
92 -
90