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Discussion Starter · #1 ·
Hi Folks,

There are a few CO2 test kits on the market. I'm not referring to the familiar drop checker. As I understand it, the CO2 test kits measure carbonic acid by titrating against sodium hydroxide and using phenolphthalein to indicate when the pH is 8.2 and above. The colour changes from colorless to pink progressing to fuchsia.

However, there are other acids that may be present in the water column, e.g. humic substances and they would presumably also affect pH but to what extent, I have no idea. So, that is the limit of my knowledge on this topic.

My question, then, is - how accurate are the test kits for measuring dissolved CO2 in planted aquaria (including fish)? Are they worth using?

I am always on the lookout for an alternative to the slow-to-respond drop checker or the KH/pH/CO2 chart. I have researched infrared absorption at 4.26 um but it is prohibitively expensive.

I look forward to any feedback.

Y.
 

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Discussion Starter · #2 ·
Hi Folks,

OK, so let me ask a different question.

Excluding carbonic acid, what other acids are present in a planted aquarium and are they present in sufficient amounts to significantly affect the pH?

I guess it may be possible to devise a set of experiments to answer this question. If I use RO water to which I add minerals bringing the KH to, say, 5°dH, what would be the resulting pH? If I were to do this outside the aquatic environment and then in a planted tank, presumably the pH would be different.

All this meandering is simply to answer my original question - if I use a CO2 test kit, will it give me accurate results?

Y.
 

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There are so many different acids in an aquarium that I wouldn't know where to start. There are various organic acids produced by the organisms in our tanks as well as inorganic ones like hydrochloric, sulfuric, phosphoric, and nitric.

This is why we use a drop checker. We can't just measure pH and kH because there are too many "contaminates".

If there was another way of doing this, I think someone would have popularized it by now.
 

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Discussion Starter · #4 ·
There are so many different acids in an aquarium that I wouldn't know where to start. There are various organic acids produced by the organisms in our tanks as well as inorganic ones like hydrochloric, sulfuric, phosphoric, and nitric.

This is why we use a drop checker. We can't just measure pH and kH because there are too many "contaminates".

If there was another way of doing this, I think someone would have popularized it by now.
Thanks, Tugg...

I value your reply - thanks!

So, there's a good chance that a CO2 test kit is not going to give meaningful measurements in freshwater planted aquaria? That's a shame. I don't like using a drop checker even though, of course, I use one in my tank. They are painfully slow to respond and not the easiest things to read reliably.

Y.
 
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