How to make your test kits go further...
Good idea. I've found it necessary to omit the water testing step for my planted tank. If I change out half the water in the tank every week, the water chemistry is always stable, so I don't have to test. Come to think of it, if I changed the tank water even more often, I wouldn't need any mechanical filtration, interesting. Another savings, but a bit more work.
I have to get out the equipment to change the water anyway, so it's pretty easy to remove a little more water. The fish seem to appreciate it and the aquatic plants are growing faster in the pure water conditions.
Water is very cheap, the testing kits typically aren't.
Just an old tank keeper's opinion, though.
"Fear not my child, just change the tank water."