Jim K wrote:

Which brand test kit(s) do you use and why? Are they accurate, easy to use,
reasonably priced?

Aquarium Pharmaceuticals for pH and KH. Cheap and accurate.

Nitrate: I have just concluded a long correspondance with Hagen over their
Nitrate test kit, which has failed on me twice. A search of usenet indicates
this is a known problem, and they have not fixed it. The third bottle has
suspended particulate matter, which jams the nozzle, which in turn makes the
test inaccurate (if you are strong enough to squeeze out the drops) or
unusable. They offer to replace the bottle if you complain, which is a good
thing, but they have known about the problem for at least two years and not
changed the design. Avoid it. People on this list recommend the Seachem Nitrate
kit. I have not tried it yet.

That's all you need if you follow the Tom Barr Estimative Index method. pH and
KH yield your CO2 level, and measuring Nitrate is important because you must
add it to most healthy plant tanks, and it is toxic to fish in high
concentrations. GH only needs to be measured if you don't know if your local
water has enough calcium & magnesium. It's easier to just ask a good LFS or an
expert local hobbiest.