Different brands of test kits is a good idea. I have always been a proponent of water changes but then I became nervous about the nutrients getting too low because of all the macroalgae growth. Now I am realizing that the macroalgae are not as impactful as I thought. This is all good things to learn before my tank took a downward turn so thank you for all you have shared. Some times I know just enough to be dangerous, ha ha!I'm sorry now that I spilled that sample of water I took when I came to visit!!
Every once in a while I would take my water to the store and test it there.
I also have 2 different brands of test kits for each parameter I'm testing also.
I still recommend you take your water and have it tested somewhere.
Always, always, when in doubt water changes are your best friend.