I used strips initially (sorry I can't recall which brands - some from Walmart, some from Petsmart) and it quickly became pricey and I discovered that they weren't giving me reliable readings. I switched to liquid after that.
The only issue I have with the liquid is remembering how many drops and the procedures because they're different for each test.
So, I ended up writing the directions on a piece of paper and taped it to each bottle. That way I don't have to keep checking the directions for each test and it's loads easier!
These days (my tanks are about 6 months cycled) I usually only test
nitrate levels when I do weekly water changes to make sure they're low and stable. I check
ammonia and
nitrite about once a month. I don't test
pH because my fish are not particularly sensitive to it. I do not suggest my testing methods for tanks that are in the midst of cycling, newly cycled, or undergoing changes like new livestock or medications. This is just what works well for my tanks at this point.
