When do you need a new electrode for your CO2 controller? - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 10-08-2011, 10:02 PM Thread Starter
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When do you need a new electrode for your CO2 controller?

Here is a clue.
When I first got my controller I calibrated the electrode every few weeks. I soon realized that this was a waste of time and just let everything go. I check my drop checker and pH read out. If they are not changing everything is okey dokey!
Recently Iíve noticed that my drop checker, which is normally blue green has switched to dark green. My pH is still 6.81. My angels and catfish are at the surface for air. I checked the CO2 level and sure enough it is at 33 ppm (my normal level is 20 ppm). Time for a new electrode! Electrodes last about a year in my tank.

If you play with chemicals you should know some chemisty.
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post #2 of 8 (permalink) Old 10-08-2011, 10:43 PM
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I would try calibrating it again. Also change the fluid in your drop checker to make sure its good too.
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post #3 of 8 (permalink) Old 10-09-2011, 12:07 AM
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Quote:
Originally Posted by ray-the-pilot View Post
Here is a clue.
When I first got my controller I calibrated the electrode every few weeks. I soon realized that this was a waste of time and just let everything go. I check my drop checker and pH read out. If they are not changing everything is okey dokey!
Recently Iíve noticed that my drop checker, which is normally blue green has switched to dark green. My pH is still 6.81. My angels and catfish are at the surface for air. I checked the CO2 level and sure enough it is at 33 ppm (my normal level is 20 ppm). Time for a new electrode! Electrodes last about a year in my tank.
I have 50-80 ppm in my tanks

Breeding fish.............

I think it would very hard to gas fish at 33ppm of CO2.........

In other words, low O2/current.....not the CO2 ............is more at play in the differences between my tank and yours.

Add more current/flow to raise the O2, this does not degas CO2 much at all.
Just enough NOT to break the surface.




Regards,
Tom Barr
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post #4 of 8 (permalink) Old 10-09-2011, 11:29 AM Thread Starter
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Quote:
Originally Posted by plantbrain View Post
I have 50-80 ppm in my tanks

Breeding fish.............

I think it would very hard to gas fish at 33ppm of CO2.........

In other words, low O2/current.....not the CO2 ............is more at play in the differences between my tank and yours.

Add more current/flow to raise the O2, this does not degas CO2 much at all.
Just enough NOT to break the surface.
I have very high current flow (which breaks the surface) and use additional aeration. My plants are continuously pearling which indicates O2 saturation.
How do you measure 50-80 ppm CO2? Also, what is your tank kH and do you have any other alkaline substances like PO4 in your water?

If you play with chemicals you should know some chemisty.
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post #5 of 8 (permalink) Old 10-10-2011, 04:37 PM
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I am on my second pH meter electrode. The first lasted a bit less than 3 years. It is a semi-consumable item.
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post #6 of 8 (permalink) Old 10-10-2011, 11:31 PM
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Quote:
Originally Posted by ray-the-pilot View Post
I have very high current flow (which breaks the surface) and use additional aeration. My plants are continuously pearling which indicates O2 saturation.
How do you measure 50-80 ppm CO2? Also, what is your tank kH and do you have any other alkaline substances like PO4 in your water?
Why don't my fish die then?
Even large full adult wild discus, they breed at 45ppm.

Pearling is NOT a function of O2 saturation.

I have very pure tap water. They do not add any phosphates and there is no non carbonate alkalinity.

CO2 is measured via silicone porous membrane if a small reference cell of about 200ul using a special flat tip probe. This flat tip reduces the lag time to under 2-3 minutes. A rubber grommet seals the reference cell and only dissolved gas can move across the membrane.

I also have an Oxyguard meter. It's fairly accurate in general.....but lag time and referencing it with their protocols is questionable, I simply just did the below:


A reference measure is taken by using a batch of RO/DI water and then made to a KH of 71.44ppm alkalinity using sodium bicarbonate. This has CO2 added via a needle wheel until I get a stable reading of 50ppm using the KH/pH relationship. This is done in a bare 10 Gal tank with about 20 liters of water.

This gets me to within about 1ppm of accuracy.

The CO2 reference cell flat tip works very well, takes 2-3 minutes to settle and then it's relatively easy. I have to add fresh solution and membranes about once a month as long as it's kept wet and in the dark.

Since the tap is also pure and I do add some PO4 as KH2PO4, but this is not alkaline......I might add a few ppm to change the KH maybe 1/2 a degree at most.

This is still a long long way off from your 33ppm. No matter how you cook this turkey, there's something else going on there. I've been keeping 30ppm or more CO2 levels since 1996. If anything..........a method to measure CO2 will always OVER estimate the true concentration as CO2 [aq], it will virtually never UNDER estimate.

Unless your pH meter is really whacked etc maybe....... There are plenty of examples of folks going back to the mid 1990's where 40-100ppm where used without issues.

I came up with a max for adult wild discus of 45ppm, they where the most sensitive of the fish species I've used/had. They turned dark and behavioral changes at that level, it was a non lethal level in other words.

A simple RO/DI water and a basically makign a good size KH reference solution, then using a freshly calibrated pH probe should suffice for adjustments to the reference CO2 method chosen. This can be done is a 5 Gal bucket etc, a scale to weight the sodium carbonate of baking soda etc.
Even if there's a little water hydroscopic residual...in 5 gal you will still be pretty darn close.

Some folks compare their tank water pH at ambient to the reference KH solution pH in a sample that's had plenty of time to degas.

Then they make an adjustment based on that difference.
Say the pH is 0.3pH units different, so instead of a 50ppm target and a pH of 6.2, they add enough to push it to 5.9.

Their 50ppm target without this correction might mean 20ppm of CO2.

This tank is 60ppm:



Not many fish, but plenty of shrimp's, gold nuggets are particularly sensitive to higher CO2, there are 3 in here.

This tank consistently has 70ppm.


Plenty of fish, but most in the pic are not that sensitive to CO2 levels at the higher ranges.

in general, PO4's do not influence pH/KH measure a huge deal, but might move them perhaps 5-10ppm.

Not 200-300% different.




Regards,
Tom Barr
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post #7 of 8 (permalink) Old 10-10-2011, 11:35 PM
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I've had long life of most pH electrodes, when I cannot calibrate them easily, or they give really off, false readings, then I replace them. If they are kept clean and stored correctly, you should get long time frames out of them. If for continuous usage, check them routinely, if anything seems off or growth has a lull, then certainly check them good. Some check monthly, which is not a bad idea, but I've known some to go many months and a few cases of year/s.

In general, I go about 2 years or so.




Regards,
Tom Barr
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post #8 of 8 (permalink) Old 10-16-2011, 01:28 AM Thread Starter
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When I first started in this analytical chemistry business a few decades ago my mentor told me that the way to know if you are getting the right answer is:
1. Know what you are doing,
2. Use the best references,
3. Calibrate everything;
4. Then check your result using a totally different method.
If the two methods agree, you can be pretty sure you are right.

I use four independent methods to evaluate the CO2 level of my water. The first is an absolute method that relies on titration using calibrated NaOH and HCl.
I measure the pH of my tank then I take a sample and immediately titrate it with-in 30 sec. (using a standardized NaOH) to 8.5. The molar amount of NaOH used is the first estimate of CO2 in the sample (to be revised later).
Then I titrate the sample with a standardized HCl solution to a pH of 4.5. I boil the sample to remove excess CO2 then if necessary add additional HCl to a pH 4.5. This solution is now CO2 free.
Now I back titrate with my standardized NaOH to the pH of my tank and then continue to a pH of 8.5.
The molar difference between the forward and backward titrations is used to determine the true kH and CO2 concentrations.
This is only one test but I confirm it 3 other ways. First my calibrated drop checker is showing dark green to blue green indicating less than 30 ppm. My pH is right for 25 ppm with low level of non specific alkalinity I have in my samples. And finally Iíve added known amounts of CO2 to my tank from a concentrated solution and find that the pH change associated with the known amount of CO2 added corresponds to the expected theoretical change with low non specific alkalinity and confirms the level of CO2 from my four parameter titration.
I am very confident of my results.

OK here is a comment about what you do.

I noticed that you only calibrate your electrode at one CO2 level. You should do at least three (and I would check at least five different levels the first time I used the device). The relationship between the measured CO2 and the actual CO2 should be linear. I would also check the device at a few different kH values especially very high kH. The reason I would do this is because I looked into getting one of the electrodes you use but the company wasnít very forthwith about explaining the chemistry so I passed.


Now what do you think is wrong with what I am doing?
One thing I am going to do is check your 50 ppm water reference and see what I get.
My feeling is that if we can get your method to agree with mine we will be very confident of the CO2 level.

If you play with chemicals you should know some chemisty.
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