CO2 measurement

[dutchy]

A good way to measure if CO2 is present would be to measure KH-PH of a sample, then let it sit overnight and repeat the measurement - this should prevent acids in the system from messing with readings - Whiskey

So how accurate wil your pH/KH measurements be? Letting it sit overnight and repeat the measurements won't help IMO because the nitric acids will still be in the sample.

Some time ago I tried the outgassing method. I measured pH with a calibrated electronic pH sensor and let a sample sit for 24 hours and measured pH again. The pH in my tank is 6,3. The outgassed sample measured a pH of 8 after 24 hours. That would mean that at a pH of 7 I would have 25 - 30 ppm's of CO2. But my KH is a measured 5, which gives me a calculated 16 ppm's of CO2 according to the pH/KH table.

All these figures tell me one thing. To inaccurate to use.

regards,
dutchy.

 

[Whiskey]

Well - that's precicely what I mean.

If you measure the PH and KH of the sample,.. then use the chart to figure out CO2 level it is a little inaccurate because acids in the water can effect these readings.
However, If you take your measurements, then let it sit over night and take them again, then use the change in PH in your calculation, then any acids that would be throwing off the readings would not change - only the CO2 has left, which helps us better isolate the CO2 to measure it.

The Drop Checker is better for an aquarium of course, but for testing a natural environment and getting real readings I think something more along these lines is better suited. But! I'm not a scientist,.. I'm just playing along to see where this discussion goes
Whiskey

 

[dbazuin]

The prof 3 e models have a automatic mode where the pomp measure the flow rate and adjust itself to get the flow rate that you have set it on.
So if you set it on a flow rate of 500 and the filter get dirty it goes faster to keep the flow on 500 until it reach its max.
In manual mode it does not measure the flow you just manually adjust it to your liking.

 

[scottward]

I have a feeling that Tom's question is more about establishing a good reference point for measuring CO2...I think?

Let's imagine for a moment that we all have one of the expensive CO2 probes, calibrated, and giving us a true indication of CO2 at a point in the water column, and we're all discussing what our 'CO2 levels' are. We need to be clear where exactly in the water column we have taken the measurement from, and this location, this 'reference point', needs to be something that can be translated accross to different bodies of water...

If 'Fred' reports that he has 50ppm of CO2 and Bob reports he has 20ppm of CO2, it would seem, upon first reading, that perhaps Fred has his CO2 sorted out and Bob doesn't. But in fact, Fred may have taken his reading relatively close to the CO2 enrichment source and his plant beds, due to poor ciculation etc, actually have very low CO2 and consequently he's having problems with algae etc. Whereas Bob may have taken his reading in the back corner of his tank where things are more static, and, by good circulation etc, his tank is actually doing a lot better.

But with so many different aquascaping techniques, flow rates, CO2 diffusion methods etc etc, how do we set up such a reference??

 

[dutchy]

What about this:

Normally the pH in my tank is at 6,3 which gives me 40 ppm on my drop checker. I have a Dennerle drop checkers which actually has digits like 0 - 20 - 40 - 80 - 120. Keeping 40 ppm on this drop checker works very well to me in growing plants and having an algae free tank. I know it doesn't say that much, but anyway.

Today I came home and found out that I had end-of-tank dump, which dropped the pH to 5,7. That's not even on the pH/KH table, which doesn't tell to much either, but it could be something like 150 to 200 ppm. Yet, no fish at the surface, not even the discusfish. Tom said they can have around 45 ppm of CO2.

Drop checker: 40 ppm. Ph/KH table: 80 ppm. pH drop because of end-of-tank dump: 150-200 ppm with no fish at the surface.

Still not confused? I am.