hoppycalif

There are only a few indicators used in pH test kits. The one that covers the 6.0 to 7.2 range is bromothymol blue, and that is what the AP test kit uses. I suspect most of the test kits we can buy use it.

hoppycalif

Here is the "drop checker" in action in the front corner of my tank. (Notice my ongoing scientific experiment with GDA - entered into solely in the interest of science.)

hoppycalif

Tom Barr has just agreed that this idea works! After a bit of disagreement over whether the KH in the "drop checker" bubble would be changed by the tank water, he conceded that would not be a problem. So, I think we have a new winner in the "most accurate way to guess how much CO2 is in your water in one easy step" contest. The little devices are still on sale on ebay too, for anyone wanting to try one, or the ADA original device should eventually be in stock, at a higher price, but probably with better quality.

newguy

thanks hoppy for the excellent followups! i guess the only thing remaining is to see how well it works long term. For example after two weeks would the indicator remain balanced, how about after a water change? would it recover etc.

hoppycalif

The proof is always in the long haul, but I don't anticipate any problem other than fading or chemical change of the indicator. Water changes wont affect it, since the water in the bulb is totally isolated from and different from the tank water. Like all testing, it becomes less and less important as the tank gets balanced, you know you have the CO2 running right, etc. But, it should be a good alarm for something drastically dropping or raising the CO2 bubble rate. And, the ebay one is pretty cheap.

This morning the indicator color is still green, to my surprise. I may need to readjust my water circulation so it moves the surface water more, and drops the nighttime ppm of CO2.

freshreef

freshreef

i have the drop checker , just need fluid

hoppycalif

BROMOTHYMOL BLUE SOLUTION
This indicates that you mix bromothymol blue crystals into distilled water, about 1% to 99% water. Apparently it isn't very soluble in water, so mixing might be a problem. You only use this stuff a few drops at a time, so why not just experiment with mixing a bit in distilled water, the adding drops to a known alkaline solution and to a known acid solution to be sure it is blue for alkaline and yellow for acid. As best I can determne, it makes no difference how much you put in as an indicator - all it affects is how intense the color is. You could even use it in the crystal form instead of as drops. It is a bit hazardous though, so don't treat it like table salt.

edit: I just found this:
Bromothymol Blue (BTB)
Bromothymol blue is an indicator, a substance that changes color as the pH of a solution changes. Bromothymol blue is yellow in acidic solutions and blue in basic solutions.

* BTB can be prepared by mixing 0.1 g (a pinch) of bromothymol blue powder in 10 mL of a 4% solution of sodium hydroxide.
* Add 20 mL of alcohol and dilute to 1 L with distilled water.
* The solution should be deep blue.
* If it is green, add sodium hydroxide solution drop by drop until the solution turns blue.
* Bromothymol blue can be purchased from scientific supply houses.

CAUTION: Sodium hydroxide is corrosive; the BTB solution should be prepared in a laboratory. BTB stains hands and clothes. Have students wear goggles and follow safety precautions when using BTB solution.

epicfish

Well, here's the science to back up the product.

Background first:
Partial Pressure of a Gas in a Liquid Gases such as CO2, O2 and N2 that are in physical solution in a liquid such as plasma, continually escape from the liquid into the gas phase and may also return to the liquid. When the rate of a gas coming out of solution is equal to the rate at which it enters the solution, the system is in equilibrium for that gas and liquid. At equilibrium, the partial pressure of a gas in gas phase is equal to the partial pressure (or tension) of the gas in liquid.

This is how the solution changes color upon it's FIRST equilibration:
Dissolved CO2 in the water will "reverse" itself to enter the small air pocket in the swan-neck of the dropcheck device. As CO2 begins to revert to it's gaseous form into the air pocket, the concentration of the dissolved CO2 in the water is still higher than that in the air pocket, so the diffusion process continues.

However, as the concentration of the CO2 in the air pocket compared to the concentration of CO2 in the indicator solution (which is 0 right now) increases, the CO2 begins to dissolve in the indicator solution, thus changing it's color.

Basically, the process is dissolved CO2 -> gaseous CO2 in the air pocket -> dissolved CO2 in the indicator solution. Any changes in the concentration of the CO2 will either cause a forward or backwards equilibration reaction.

The biggest drawback to this is the delayed response of the solution to the CO2 levels. Diffusion and dissolution rates of the CO2 depends on many factors: water temperature, air pocket temperature, atmospheric pressure, water circulation around the indicator device, and last but not least, how long the indicator solution has been sitting in the bulb. Since the solution is bromothymol blue sitting in sodium hydroxide (NaOH), be real careful of it. Do not over-fill the bulb. Even though it's a real dilute solution, better safe than sorry.

The MSDS here says the indicator solution should be relatively stable. MSDS :: Bromothymol Blue 0.04% w/v Aqueous, however, if the water temperature is in the higher range, condensation in the air pocket could drip into the indicator solution, thus changing it's concentration, and possibly it's accuracy. This isn't very likely though, because the entire apparatus will be at the same tank water temperature.

Original Kuhli

Condensation is only possible if there's a delta/difference in the temperature of the glass to the aquarium water.

This should only be the case on initial installation, so as long as you put warm solution into the drop checker there should be no possibility of modifying the drop checker kH via condensation.