Co2, Ph And Other Such Oddities

[Themuleous]

Hey All,

There have been several threads/posts recently on pH affecting everything from CO2 concentration, how CO2 charts dont work, phosphate buffering, iron becoming unavailable at high pH, etc and just wanted to start a thread so we can share our own experiences.

Ill start by saying that, I thought I was running my CO2 at 30ppm, as my 6KH and pH of 6.6 would give me 45ppm according to the charts, however I have been told several times that the charts are not as accurate and that a better way to test is to test the tank water after its been sitting for 24hrs and try to obtain a 1 point pH drop in the tank as this should give you the 30ppm CO2. I recently tested this theory and found that I was no where near 30ppm. My sitting water was pH 7.4, but my tank was 6.6. So not the 1 point pH drop needed. So have upped CO2 bubble rate and now have the pH more like 6.3/6.4. Which according to that chart gives me a CO2 of 70ppm! I wont even try to explain this, but that's what I have found.

As many of you will know I have huge algae problems in my nano which could be explained (as Tom Barr raves about) by low CO2. I will in future be ignoring the pH charts!

Anyone else got any helpful advice/tips and hints? Choose a subject and let everyone else know!

Sam

 

[BigIan]

does the "standing water" method work even if you have substrates ect that alter the water chemistry???

 

[Themuleous]

Yeh should do, but perhaps not with the ADA soil as that actually removed KH, but don't know. I guess it should still work, providing you can measure the pH below 6, which most off the shelf kits cant, so you might need a pH probe meter.

Sam

 

[MoreCoffee]

Sam,

Any chance you can provide a link or clear description (an 'idiots guide' would suite me ) about the 'standing water' method for CO2 measurement ?

If nothing else, I'd be interested in doing a comparison between methods.

Thanks

Al

 

[Themuleous]

Dont know of a link Al, but put simply do the following.

1) Fill a pot with tank water

2) Put the pot somewhere safe and let it sit for 24hrs, I stir mine a few times to help get rid of the CO2 but dont thinks thats vital.

3) Test the pH of the water in the pot.

4) Test the pH of your tank

5) Compare the two! Im told a 1 point difference means you've got 30ppm CO2

6) Relax with a cold beer and feel very pleased with yourself that you've got enough CO2 in the tank

Easy as that my friend! Let me know what you find out, I was unpleasantly surprised when I didn't have the 1pH difference despite what the CO2 charts were telling me.

Sam

 

[BigIan]

Yeh should do, but perhaps not with the ADA soil as that actually removed KH, but don't know. I guess it should still work, providing you can measure the pH below 6, which most off the shelf kits cant, so you might need a pH probe meter.

Sam

in theory it should work, as the co2 should make the diffrence no matter what the kh of the water is,
i`ll give the tank a week or two to settle first (plus i`m still waiting for my co2 to be deliverd almost 2 weeks late now) before i try testing.

 

[MoreCoffee]

Dont know of a link Al, but put simply do the following.

1) Fill a pot with tank water

2) Put the pot somewhere safe and let it sit for 24hrs, I stir mine a few times to help get rid of the CO2 but dont thinks thats vital.

3) Test the pH of the water in the pot.

4) Test the pH of your tank

5) Compare the two! Im told a 1 point difference means you've got 30ppm CO2

6) Relax with a cold beer and feel very pleased with yourself that you've got enough CO2 in the tank

Easy as that my friend! Let me know what you find out, I was unpleasantly surprised when I didn't have the 1pH difference despite what the CO2 charts were telling me.

Sam

Thanks Sam,

I'll give this a try later this week. I've just done a 50% water change, so will wait a day or two before taking a reading.

It certainly makes sense that the PH will change once the CO2 has disipated from the water, but never heard the relationship between 1 ph level being equal to 30ppm before.

 

[Themuleous]

Nor had I til Zig pointed it out a few months back. Definitely worth a try.

Sam

 

[RadaR]

Interesting.
Ill give it a go Sam and get back to you.
Off to do a water change..

 

[MoreCoffee]

Nor had I til Zig pointed it out a few months back. Definitely worth a try.

Sam

Thanks again Sam....

Zig: Any further info you can add to this ?

 

[George Farmer]

Top post Sam. I'll add this to the pinned CO2 thread.

Dont know of a link Al, but put simply do the following.

1) Fill a pot with tank water

2) Put the pot somewhere safe and let it sit for 24hrs, I stir mine a few times to help get rid of the CO2 but dont thinks thats vital.

3) Test the pH of the water in the pot.

4) Test the pH of your tank

5) Compare the two! Im told a 1 point difference means you've got 30ppm CO2

6) Relax with a cold beer and feel very pleased with yourself that you've got enough CO2 in the tank

Easy as that my friend! Let me know what you find out, I was unpleasantly surprised when I didn't have the 1pH difference despite what the CO2 charts were telling me.

Sam

 

[Themuleous]

Cheers George! Quite chuffed at that, made my day

Sam

 

[MoreCoffee]

Does anybody have any other info on this. Particularly confirming that a PH drop of 1 point = 30ppm.

I dont doubt the theory behind it, just looking for some confirmation on the figures !
If they are accurate, I'd certainly use this method over a CO2 chart (thanks to Sam for posting it)

Cheers
Al

 

[Themuleous]

No probs Al. I know what you mean about the confirmation of it working. As if a 1 point drop does equal 30ppm CO2 then the charts we use are way off. As I said originally to get the 1 point drop in my nano I need a pH of around 6.4 with my 5.5KH, which according to the charts is 65ppm CO2, they cant both be right! Maybe there is some truth to the fact that the lower the pH and/or the KH the more CO2 you need to bubble into the tank to get 30ppm, who knows!

Anyone able to confirm?

Sam

 

[JamesC]

Does anybody have any other info on this. Particularly confirming that a PH drop of 1 point = 30ppm.

The theory behind it is fairly simple. What it is doing is removing the need to measure the KH and so also removing the inaccuracy of the KH measurement. What we need to do is start with tank water with the CO2 at equilibrium with the atmosphere as this will give us a pretty reliable figure of about 3ppm CO2. The pH of this is then measured. Look at a CO2 chart and find the pH you have just measured and also where the CO2 equals 3ppm at this pH value. Now staying within the same KH value move along until you find the CO2 value of 30ppm. This you will find will be at a pH value of 1 below your earlier reading. This is then the pH you need to aim for to achieve your 30ppm CO2.

For example if your standing water has a pH of 7.4 then when CO2 is 3ppm then KH is 2.5. So staying at KH=2.5 we find where the CO2 is at 30ppm which is at pH=6.4. Doesn't matter where on the chart you try this it always works out at 1 pH value lower.

James