Ok, so I have been following the post about Drop Checkers and pH probe mods and decided to go ahead and order a Drop Checker off of E-Bay (looks just like the ADA one)... Now that I have it and am faced with the actual task of setting it up and making the kH reference solution, I have a few questions:

- Cleaning the drop checker before use - I am assuming that a few rinses in the huge amount of kH solution that I will end up with would be sufficient?
- The water - Is "Distilled" water the same thing as "Deionized" water?
- The test regent - Is there a certain pH test regent that is best for this application? The regent that came with the kit was open in transit and had to be thrown away. I am considering using my AP pH test regent... Will this work?
- Refreshing the solution - How often, if ever. should I change the kH reference and Regent to maintain accuracy?
- Shelf life of the kH mix - Since I will be mixing 5 liters of this stuff, can I leave it in my garage for future use? It can get hot in the summer and cold in the winter... Just not sure about the storage of this solution.

Once I have my kH solution baked up, mixed and measured, I plan on using it in the AP kit's pH test, then using that liquid, which will include the regent, to fill the drop checker. Does this sound right?

TIA

Congratulations for deciding to go with the drop checker!
Either distilled or deionized water will work for the KH solution - neither should have any ions in them that affect alkalinity or acidity.
AP test reagent is just fine, as are any of the test reagents for pH that give a yellow to blue range of colors as the pH goes from about 6.2 to about 7.2.
I am finding that the solution in the drop checker bulb will last for at least two weeks, but the water level continues to rise slowly in the tank end of the "funnel" as the air is slowly absorbed by the water. So, I suggest the best idea would be to change the fluid every two weeks.
Water with a little baking soda in it shouldn't have a "shelf life" as far as I can see. As long as the water doesn't start evaporating, thus raising the KH, it should be good for a long time. I do know that a gallon plastic bottle of drinking water will shrink in a year or so, so apparently there is evaporation through the pores of the plastic. But, a glass bottle, with a sealed cap, should last forever.
The way I have been filling that drop checker is by using a syringe with the needle bent about 20 degrees. I squirt in the water to the level I want, then add a drop of reagent, and if the color is still too weak I add another drop. The number of drops isn't critical, but if you get too much the bulb just looks like opaque blue-black ink. Much better to have some transparency. Getting the liquid back out of the bulb is also a challenge, which a syringe helps a lot with too. And, washing the bulb with standard KH water works easier using the syringe.

Thanks!

One question on the Drop Checker liquid replacement every two weeks... If I am doing 50% PWC every saturday, the air gap would be automatically reset, so I don't believe that would be an issue. Is that the only reason you change it every other week? I was hoping to not have to mess with it more than monthly (ideally less often than that).

I'm not relying on it for anything right now, since I have already set my bubble rate to get the green color. So, I am just leaving it in the tank out of lazyness right now. If I wanted to rely on it again I would change the solution in it. Like any other object in the tank this begins to get "biofilm" growing on it too, so it needs to be cleaned periodically. Mine is in a very low light corner of the side glass, so the growth of "biofilm" (sounds so much better than algae) on it isn't bad at all yet.

When you put it in the water, do you try and minimize the air gap by letting some water up the glass a bit, or is it alright to leave as much air in there as possible?

I don't know. The larger the area of the water-air interface, the faster it will respond. But, the smaller the volume of the air gap, the faster it will respond. My guess is that it makes no practical difference if the water is up in the trumpet a few millimeters or less than one millimeter. If the water level is too high in the trumpet, the local CO2 concentration in the tank water may be slightly lower, making the drop checker read low, but that effect may be very slight.