epicfish

30 ppm = optimal.

hoppycalif

It is hard to know what the best ppm of CO2 is, since the numbers people use are all based on measuring pH and KH of the tank water, which is not an accurate method, due to the other things besides CO2 that affect acidity and alkalinity in our tank water. You can choose the ppm of CO2 you want the indicator to be green at, by adjusting the KH of the distilled water in the bulb. I picked 30 ppm believing that to be at least not too much. For that I used KH=4.0 in the bulb. I am thinking about raising the KH to maybe 5 later, to get green at 40 ppm, and if that is still ok, going to KH of 6 to get green at 45 ppm. This would be a way to finally determine what the "best" ppm of CO2 really is.

Gatorguy

So what are you doing to make the "solution" 4 dKH?

So you want the "solution" in the drop checker to be 4 dKH, then you add a pH regeant so that you can "see" the pH change in the solution as it is exposed to more or less CO2 that is diffused from the aquarium through the air gap and into the solution?

I must be missing something. 4 dKH and "green" (my test kit is pH 7 at green) would only be 12ppm. Where am I going wrong?

I'm probably fixing to order one of those drop checkers from eBay. Why not?

hoppycalif

Here are the color charts for the three commonly used pH test kit reagents. For the top one, it is yellow at pH of 6.0, blue at 7.2, and green (the middle) at 6.6.

wantplantsnotwork

Can someone please explain (in steps for this short bus rider!) exactly /how this works / how to use it?
Does that green test solution ever migrate into the tank? If it ever did, what happens?
Thanks!

claire09876

Hello,
I'm very new to all this. I'm not sure what you mean by distilled water for your drop checker and why that's important. Could you explain please? I'm assuming from your discussion that you can change the KH of this by adding bicarb of soda. KH is the water hardness right?! So it will be very different depending where you live in the counrty (I'm in the UK).

Sorry new to website and didn't realise there was more after 1st page!!!! Maybe there are answers in the other 19 pages!!!! Sorry if I have interupted your discussion on something else.....can I delete an entry and how?

Thanks
Claire

Squawkbert

You use distilled water to make your 4dKH solution. If you use plain water, pH could be off as a result of something other than the bicarbonate.

PS - for you "real chemists" 4dKH corresponds to 0.06648mM Na Bicarbonate (if my math is right).

hoppycalif

This works because a sealed container of air in contact with water will reach an equillibrium amount of CO2 that is at least proportional to the ppm of CO2 in the water. So, two containers with their water in contact with the same sealed container of air will reach the same ppm of CO2. The "drop checker" has distilled or DI water in it, with a known KH obtained with bicarbonate only - no other source of alkalinity, and no source of acidity. That makes the equation that is behind the pH/KH/CO2 table work correctly (see Chuck Gadd's website). So, if we can measure the pH of that little bit of water in the "drop checker", and we can, by using a pH indicator solution, we can accurately calculate how much CO2 is in that container of water, which will be the same as is in the tank water, since they are connected with a sealed air column. At KH=4, and 30 ppm of CO2, the pH will be 6.6 which turns the bromothymol blue indicator, used in almost all pH kits, green. So, green means you have the right amount of CO2 in the water, and yellow green means you have too much, while blue green means you have too little.

There is no way for the indicator solution to migrate to the tank water, since there is an air gap separating it from the tank water. If it did get into the tank water, it would be about 4-8 drops of a 4% sodium hydroxide in water solution with a little bit of bromothymol blue dye in it. It wouldn't be desirable to have it mixed into the tank, but I doubt it harming anything if it were mixed in.

So, to use this:
First, get some distilled water from the grocery store.
Using clean glass container, pour about a cup of that water into the container.
Next, add a very small amount of bicarbonate of soda - baking soda - Arm and Hammer soda, etc. to the water and stir it up with a very clean stirrer.
Test the KH of that water with your test kit.
Most likely it will be a higher than 4 KH. So, add some more distilled water and repeat the test. (If the first KH comes out to 8 degrees KH, double the amount of water. If it is 6 degrees of KH, add 50% more water, etc.)
When you get close to 4 degrees KH, repeat the test using twice as big a water sample in the vial as the kit calls for, then count each drop of KH reagent as being half the degrees of KH that the kit normally says - for AP test kit, that makes each drop equal to .5 degrees KH. I found I can get very near "exactly" 4 degrees KH by doing this carefully.
Use a syringe to squirt some of this 4 degrees KH water into the bulb of the "drop checker". Fill the bulb about 2/3 full of the water.
Add a few drops of your pH test reagent - use enough to get a strong blue color, but not so much that the water becomes opaque with the blue dye.
Use the suction cup on the "drop checker" to suspend the device two or three inches below the tank water surface, with the "horn" of the "drop checker" pointing down so it traps air in the horn.

After a couple of hours or so the color of the "drop checker" fluid will be at about the equillibrium color, and that should be green if you have 30 ppm of CO2 in the water. If the color is yellow, you have at least 70 ppm of CO2 (and your fish are in serious trouble!). If it is blue, you have about 10 ppm of CO2, which is not nearly enough.

wantplantsnotwork

Thanks for taking the time to get that out Hoppy, I appreciate it!

Gatorguy

Yeah Hoppy, thanks! That is what I was fishing for in my last post. Wantplants asked in a better way than I.

Thanks!!