Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I get the test strips from whichever on line store has them the cheapest. Usually 100 in a bottle for the same price as the stores sell for 25-in-a-bottle.
I do get odd results once in a while, but I can generally see the color change in the API test kit. But it is the first one to die of old age. Then, no matter how many drops you add there is no color change.
By comparing tests from prior weeks I can tell if something is changing in the tank. Not so much the actual number (I think we all agree the tests are not great at that) but the trend. If the water is gradually getting harder in the tank then I know to do bigger water changes.