That's a relief - I can tear up the high school enrolment papers now!

Next issue: does anyone know if the indicator (dye) fades with continuous exposure to aquarium light intensity? My indicator is a greenish golden color now - meaning about 45 ppm of CO2, but it is not intense enough to satisfy me, and I have about 12 drops of reagent in the mix. (I'm using the Aquarium Pharmaceuticals reagent instead of the tiny bottle of stuff that came with the device.) Maybe I should try the cheapy reagent next. It seems like there would be a maximum amount of reagent you could mix with the water without changing the chemistry - I think it has sodium hydroxide in it.