Even if I poke into a hornets nest now, I have to state that it's not absoulutely necessary to test your pH and kH for the
CO2 values all the time.
It's great to have test kits at home, I have them myself and test the water frequently. The only thing is that if he would go and get his tab water and aquarium water, before and after
CO2 injection tested at the
lfs, you shouldn't need to test all the time with a store bought kit like that.
I had a kit from Dennerle before and it worked absoulute constantly and without any kind of problems at all.
If he decides to make his "own" mixtures - then yes, I would advise to get a test kit, to see when you are getting close to producing too much
CO2, exspecially for a small 10gal tank. I have experiemented with
DIY mixtures myself and had everything from nearly no production to a
CO2 blowout within 2 days. And still the system Travis wants to use has a passive reactor and therefore should not be able to diffuse too much
CO2 into the water anyway.
Hence, I think it's only necessary to test the water frequently to figure out the
CO2 saturation, if he wants to use his own mixtures, instead of going with the "regular" ones. And still a complete water test kit is really worth an investment and should be considered anyway, not only to test the
CO2 saturation.