hoppycalif

I wait with bated breath to see what the effect of 45 ppm of CO2 is on the fish and shrimp. (No, seriously, I plan to take a breath now and then.) When I first set up my ebay dropchecker the color went to yellow pretty quickly, with 4dKH water in it. And, all of the fish were gasping at the surface. So, I think there is a narrowing range of higher ppm's available to check out. Once I get my GDA problem solved for good, and my aquascape fixed - too much hygrophila now - I will switch to 6 dKH water in mine, to see if 45 ppm works for me.

dennis

I finally got some distilled water and made up some kH 5 water. Here is what I found to be easiest: 6grams NaHCO3 raises 50 liter of water ~4 degrees. I can acurately measure 500ml so 4degrees in 500ml is .06gram. Now, my gram scale has a readout of .1gram so to get a nice round number, .06*5=.3g. So, add .3 gram to 50ml of water. That way, 10ml of that solution (suck it up with a syringe) in 490ml water is about 4 degrees. Test with Lamotte reads 4.04 degrees. So, add 2ml more and test again. kH=5 degrees.


I have a confusing issue now though. I mixed a small dropper bottle of this solution with 2drops per ml of indicator and filled my little drop checker. I also used the same 5kH mix w/o indicator to fill my electronic drop checker. I had calibrated the probe yesterday but the electronic checker settled overnight at a reading of 6.1. The color checker is blue green. There is definitely a big descripency but I can't think of what the problem may be. My initial thought is that the probe end, which absorbs water is effecting the readout.

Maybe I should soak my probe in distilled for a while to try and pull any kH in the probe out by osmosis. Also, I am wondering if I should use a lower kH in the electronic version since it may make the gas transfer happen faster- lower kH means biggger pH swings. I am thinking I should buffer to .5-1 degree for that.

Any thoughts?

hoppycalif

I have been thinking about the electronic version - the "requirements" for the solution in it are much different from that of the indicator solution version. The latter needs water with a KH of 4-5 dKH so that the color will be green at the CO2 ppm that is desired. But, the electronic one doesn't have that need, so for that one it is best to set the KH to where the pH will be about 7 at the desired ppm of CO2, and that is at about 13 dKH. (Because most pH probes are calibrated to be right on target at 7.01 pH.) I don't understand how a pH probe works well enough to be able to figure out why your reading seems to be off. My pH probe has always been so erratic that I don't trust it at all, and it is too bulky to be used for a drop checker anyway. I just wasted my money when I bought it.

dennis

I'm not sure about that. A kH of 13 woudl mean you inject lots of CO2 before getting a pH change. That means you would OD you tank on CO2. I think better would be to use a very low kH so that the pH change happens fast and easily, allowing the controller to be more in control. I do not think it matters if the probe reading is at 7 or at 5, it will still be as accurate as the probes accuracy. What I mean is, I do not think that having a lower pH as the setpoint will compound any probe inaccuracies. Therefore, a lower kH will mean a faster response time... I think.

hoppycalif

With a 13 dKH water reference you get:
pH - 6.6 = 100 ppm CO2
6.7 = 80
6.8 = 60
6.9 = 50
7.0 = 40
7.1 = 30
7.2 = 25
7.3 = 20
7.4 = 15
7.5 = 10

The amount of CO2 introduced into the tank wouldn't be affected by the KH of the drop checker water, nor would the amount of CO2 to be absorbed by the drop checker be affected. The goal should be to make the KH be such that around the ppm of CO2 you want, the changes in pH per change in ppm of CO2 are a maximum. At a KH of 1dKH you get:

pH - 5.5 = 95 ppm CO2
5.6 = 75
5.7 = 60
5.8 = 50
5.9 = 40
6.0 = 30
6.1 = 25
6.2 = 20
6.3 = 15
6.4 = 10

So, I conclude that the only effect of KH is to shift the pH range that is of interest, and it seems to me that the closer that is to 7.01, where you do a one point calibration, the more accurate the pH probe/meter is. (All of the above ppm values are rounded off to the nearest 5 ppm)

I also manipulated the equation for ppm vs KH and pH to find at what KH the change in pH vs ppm is a maximum - and, as the tables above show, the change in pH vs ppm is not dependent upon KH.

wiste

How long do you leave the drop checker in the tank? I understand there is a minimum time that you have to leave it in the tank but I am curious to know if you leave it in the tank over a long period, days or even weeks and use it like a thermometer.

epicfish

Yes, it's held in there with a suction cup indefinately so that you can always glance over at it and know approximately what your CO2 levels are.

hoppycalif

Yesterday I learned that Dennerle makes this device, complete with reference solution with indicator reagent in it. They call it "CO2 Long Term Test Correct" and it is made of plastic. The reference solution (distilled water with bicarbonate in it?) has a KH of about 3dKH, to give a green indication at 20-25ppm of CO2 in the water. The configuration looks to be about that of the teardrop shaped glass one that is sold on ebay. So far I haven't seen this device for sale in the US, but it is in the UK and Europe.

Based on Dennerle's instructions, the solution in the device needs to be replaced about once a month because the indicator, which is a dye, will fade with exposure to light over that period of time.

I suppose in a few weeks someone will point out that Leonardo da Vinci first invented this device back a few years ago!

wiste

Try a web search for ‘Dennerle CO2 Visual Indicator’. If this is the same product it is available.

hoppycalif

Yes, that is it! For some reason I couldn't find those suppliers when I googled it yesterday. $17 plus shipping - not too bad unless the shipping cost is exhorbitant.