Last week I took a trip to Tap Plastics, where I bought a 1" dia, 1/16" wall thickness acrylic tube, to go with my existing 5/8", 1/16" wall acrylic tube, and some acrylic disks - 1", 1/2", 5/8" diameter, plus a tube of medium viscosity acrylic cement. Then I spent a couple of hours yesterday and a couple of hours today, using only hand tools plus a cordless drill to make a couple of DIY drip checkers. The first one is probably the fastest reacting one:
The second one is probably the easiest to read the color on. I used white fingernail polish to paint the inside of the air gap tube which becomes the background for the fluid in the bulb.
Tomorrow I plan to load both with distilled 5 dKH water and reagent and place them in the tank at the same time, to see how they compare. I will post those results, too.
Edit: Today I loaded them and added them to the tank.
Edit: After two hours all three of the devices have the same color. The one with the white background was the slowest to get started with the color change, by a half hour or so, but once they were all changing color, both of the DIY ones ended up with the green color at about 2 hours. Now, I'm not sure what affects the response time of these, but I am sure that both of these DIY designs work well. (Both of these have been spoken for now. Maybe someone else would like to start making these and selling them here?)