Another CO2 Chart to try - Page 2 - Fertilizing

Glouglou · 03-16-2006, 04:16 PM

Hanns-J Krause CO2 Test
Author Handbook Aquaria Technology
Krause recommends a different method to measure CO2 content. That method is insensitive to the presence of unusual buffers.

Step 1:
Take another water sample with some pH indicator and run the hose from an air pump into the sampe for a few minutes. This sets the CO2 level at 0.6ppm.
—>Measure pH of the water (=X).

Step 2:
Take small water sample with some pH indicator. Stick a straw into the water and exhale through the straw into the water sample for two or three minutes. This sets the CO2 level at 60ppm.
—>Measure pH of the water (=Y)

Step 3:
The optimum CO2 concentration of 10-20ppm is at the pH value about 2/3 of the difference between X and Y:
pH,optimum = X +.67*(Y-X).

As an example, if you measure pH 8 with the first sample, and pH 6.5 with the second sample, a tank pH of 7 corresponds to 30ppm CO2, regardless of any buffers that might otherwise confuse a CO2 test or distort the charted values.

dkfennell · 03-17-2006, 03:19 AM

Gouglou, if we assume de-gassed aquarium water has concentration of .6 ppm CO2 (from Henry's Law, assuming room temperature (?), and sea level (?)), then why in sample (I assume also from the aquarium) do you add additional CO2 (from breath) and make an assumption about the concentration of CO2 in that water (before testing pH)? Wouldn't simply testing the actual aquarium water, as guaiac_boy long ago suggested, and using MarcosB's equation (on page 3 of this threat) be a better approach, at least, for no other reason, one fewer assumption is made?

The only argument I can see in favor of your approach is that the wider gap in pH difference in your test makes testing the difference (which color pH tests) slightly easier (or, perhaps better, the larger difference makes the imprecission of the color tests contribute less error to resulting estimate). But I don't see how that compensates for the additional assumption.

Darrell

**IUnknown** · 03-22-2006, 07:24 PM

You could adjust the chart to compensate for any buffers in the tank
using Tom's suggestion. I need to dial in the Co2 on my new tank, so I'm
going to try a couple of these methodes to see how they compare. The
one thing I need to look into (I'll report back if I find an answere) is
how the Co2 test kits work (Like Amano's eye dropper, or the lamotte
kits). Are they affected the same way?

Quote:

You can do a dirty little method to figure out your CO2 relatively close(pH is log scale though but this method is close enough in general)

Take a tap water sample, lt it sit 24 hours, measure pH/KH, should be about 3.7ppm CO2 or so.

Take a tank water sample, let it sit for 24 hours, take a pH/KH reading. Assume the CO2 content in both are equal.

Take the difference in the pH, say 0.4, add that from the tank reading.

So a pH of 6.4 is really 6.8 etc.

This is not perfect, but it's doable and relatively close.
You can transform the scale to log scale to get a closer approximation but the accuracy gained from all that is still low.

But since folks do large water changes, the humics are really regulated to the substrates and much less so to the water column after a few water changes.

I highly recommend for folks like you guys to do the add enough CO2 to get the plants all happy and then a little more, I hate controllers personally.

Test kits and other things cause more problems in some ways.
Simple is good. I'm still leary of suggesting this method though to new folks, I've seen dead fish tanks and if you kill the fish, I do not care what folks say, that's bad advice if there's a high risk of a new person doing that.

Many folks in Asia do that

I see many post on that. I see that here in the USA also. But I suppose it's better than algae? hehe
Amano's done it too. I've been lucky, I killed some shrimps once, no fish to date yet.

Regards,
Tom Barr

Edward · 03-27-2006, 07:35 PM

Y = gassed tank water 6.5 pH
X = degassed tank water 8.0 pH
__________________________

at 1 KH, 10 ppm CO2 - 0.3 ppm CO2 = 9.7 ppm CO2
at 5 KH, 49 ppm CO2 - 2 ppm CO2 = 47 ppm CO2
at 10 KH, 97 ppm CO2 - 3 ppm CO2 = 94 ppm CO2

So what is it, 9.7, 47 or 94?
How does the X + 0.67 x ( Y – X ) help here?

BryceM · 03-28-2006, 05:31 AM

Quote:

Originally Posted by Edward

Y = gassed tank water 6.5 pH
X = degassed tank water 8.0 pH
__________________________

at 1 KH, 10 ppm CO2 - 0.3 ppm CO2 = 9.7 ppm CO2
at 5 KH, 49 ppm CO2 - 2 ppm CO2 = 47 ppm CO2
at 10 KH, 97 ppm CO2 - 3 ppm CO2 = 94 ppm CO2

So what is it, 9.7, 47 or 94?
How does the X + 0.67 x ( Y – X ) help here?

I'm not sure I understand your question...

If you change the KH of the water, the water's degassed pH will change too. You can't make the assumption that the degassed pH will remain constant at differing pH values - it doesn't.

Right now my tank has a KH of 4, a degassed pH of about 7.4 and a 'gassed' pH of 6.4. This makes by pH drop about 1.0 units.

If I were to add some NaHCO3, my KH would go up, and degassed pH would also go up. My target pH would also then go up, since I'd be achieving my 1.0 unit drop at a higher pH. If I still aimed for 6.4, my CO2 concentration would be higher than before.

Or am I completely missing the point of your post?

RTR · 03-08-2006, 09:22 PM

hoppycalif - that particular old timer is also the only person I know of who worked out the equilibrium levels for CO2 from air, with compensation for altitude/barometric pressure. Check out his web site, it has to be there somewhere, or on The Krib, or both.

MarcosB · 03-09-2006, 05:06 AM

I think that 3 ppm is far from the true value of the equilibrium.
A simple calculation using Henry´s law gives a value of 0,5 ppm of dissolved CO2 in equlibrium with atmosphere.

yildirim · 03-09-2006, 01:01 AM

Hello friends,

Aren't you still bored of this CO2 conversations. Yes it is a must for all planted tanks but measuring the level is very tricky as there are many factors affecting all the variables. So you can not be sure that the level you read from any of the tables is 100% accurate. What I do is always try to keep it as high as possible and the only indicator for me is fish distress.

YILDIRIM

John S · 03-09-2006, 05:29 AM

i agree with YILDIRIM i run my co2 as high as i can get away with as long as you are above 30 ppm u are going to be fine let the fish tell u how high it is lol. everyone gets to hung up on spot on testing.

MatPat · 03-09-2006, 07:14 AM

Quote:

Originally Posted by John S

i agree with YILDIRIM i run my co2 as high as i can get away with as long as you are above 30 ppm u are going to be fine let the fish tell u how high it is lol. everyone gets to hung up on spot on testing.

I agree with both of you on the testing. Even with good kits and meters there are some variables, not to mention human error, and no one test will be perfect. I rarely test unless something appears to be wrong but this can be a difficult concept to grasp for those without much experience. When you are new to the hobby, it is nice to have some "numbers" to go by until you gain a bit of experience.

According to the KH/pH chart, my levels are over 200ppm (LaMotte Alkalinity test and Hanna 98129 meter) and if I were to follow the advice at keeping my levels in the 30-40ppm range, I would have massive BBA in my tank. Go ahead and ask how I know this

My fish do not gasp at the 200ppm range (90ppm with Hoppy's method) but new fish succumb very quickly to these levels. I have been increasing the CO2 very slowly for a long time now and it appears that the fish may be able to adapt somewhat.

Raising the CO2 levels can be very dificult for someone new to the hobby to understand. I myself was a victim of this when I first started following the advice of folks to increase my CO2 levels. Go ahead and ask how I know this too

I think what Hoppy and the rest of us are trying to arrive at is a simpler way for beginners to determine CO2 levels and not kill off their fish!

If a new method can help only one person get into the hobby and stay here, then I think it is a worth while discussion