Another CO2 Chart to try - Page 3 - Fertilizing

MatPat · 03-09-2006, 11:59 AM

Quote:

Originally Posted by Bert H

I can't see the chart, just broken link symbol.

The link seems to be working now. Maybe we can persuade Hoppy to add it to this site.

BryceM · 03-09-2006, 12:17 PM

One word of caution......... It's still important to keep an eye on the KH, especially if you need to supplement NaHCO3 due to very soft tapwater. My tap KH is <1. If you let it get too low, you risk a pH crash. Also, both your degassed CO2 levels and your tank CO2 levels will be quite low. Fish can compensate for elevated CO2 levels using certain metabolic pathways, and they can compensate for gradual changes in osmotic load, but at some point they just can't compensate for living in acid. Once pH starts getting down into the high 5's I think you'll see problems in most fish and some of the plants we keep.

IMO a KH of at least 3, seems prudent. I keep mine between 4 and 5.

Also, many people are reporting recently that they maintain enormously high CO2 levels to battle BBA. Their fish seem to do just fine, but when they add new ones they go into shock. It's probably something like opening the window of an airliner at 28,000 feet - people pass out pretty quick without O2, yet climbers have done Everest (29,035 feet) without O2. The trick is a gradual ascent over several weeks to allow the body time to compensate. Introducing new fish might become difficult, making a gradual transition mandatory.

Navi · 03-09-2006, 01:53 PM

It seems to me this theory is totally based on an assumed equilibrium of 3 mg/l. That's a big assumption IMO. If the assumed equilibrium was off by 1 mg/l either way, the chart would be totally invalid.

Or am I missing something here?

MarcosB · 03-09-2006, 02:13 PM

Under normal circumstances the CO2 equilibrated with the atmosphere should be 0.5 ppm, and the equation to determine its concentration as a function of pH variation before and after aeration is: [CO2] = 10^(pHdiff – 0,3).

banderbe · 03-09-2006, 04:30 PM

Quote:

Originally Posted by MatPat

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

Ditto, I have 86 ppm CO2 according to the charts, and I know for a fact that my KH is 18 (city water report and confirmed by test kits) and I am reasonably sure my pH is at or around 6.8 (AP and RedSea kits agree).

But, three of my fish died last week. Oddly the others were fine and never showed any signs of stress.

R0bert · 03-09-2006, 04:39 PM

Quote:

Under normal circumstances the CO2 equilibrated with the atmosphere should be 0.5 ppm, and the equation to determine its concentration as a function of pH variation before and after aeration is: [CO2] = 10^(pHdiff – 0,3).

MarcosB can you show me how you arrived at 0.5ppm? I worked it out even lower than that, but I'm not certain about my constants.

hoppycalif · 03-09-2006, 04:48 PM

We should be able to measure the equilibrium concentration of CO2 when a water sample sits open all night, by using distilled or demineralized water, with a bit of baking soda in it for KH. Doing this for a couple or so different KH's should settle the question on whether this method is at all accurate. I plan to try this tonight, but I hope others can try it too. A gallon of distilled or demineralized water is pretty cheap.

MarcosB · 03-10-2006, 04:01 AM

Robert
The composition of CO2 in atmosphere is ca. 380 ppm (0.038 %) which gives a partial pressure of 0.00038 atm. The Henry´s law constant for CO2 is 3.38x10^-2.
Thus, using the Henry´s equation we have:[CO2]aq = 0.00038 x 0.0338 = 1.3 x 10^-5 mol / L of CO2.
Converting to mass:
1.3x10^-5 x 44 = 0.00056 g/L= 0.56 mg/L (ppm)

R0bert · 03-10-2006, 04:52 AM

Thanks MarcosB. I made a mistake with the mass conversion.

The last post in this article explains the method quite clearly: http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

MiamiAG · 03-10-2006, 05:13 AM

Hobby,

Just upload the chart to our Photo Album and link to it from there. Our image hosting is free to members.

Excellent discussion by the way.