I have a ten gallon tank that will be home to a betta in a few weeks, when I move back to college and get everything set up. I'm still gathering essentials like a heater, substrate, and things like that, and I'm stuck on what kind of test kit I might need to purchase.
My dad, who has kept several large tanks before with varying numbers of fish (he's decently experienced with fish keeping), suggested to me that I might not even need to test the water unless something appeared to be going wrong, because with just one fish in a 10-gallon tank, there wouldn't be much of a chance of an ammonia spike at all, once it was properly cycled and everything was working alright. But I still wonder if it'd be a good idea to buy the API Freshwater Master kit anyway, just to be on the safe side. I'd probably need some kind of test kit for the time when I'm first cycling the tank, right? Just to keep up with the different levels of ammonia/nitrate/nitrite in the water? I figure it'd be a better monetary deal to spend more on the whole Master kit than just a bottle of the test strips, because the Master kit would last much longer if I ever needed it.
Different chemicals can spike at different times based on water params and how healthy your fish is. It's generally advised to test while cycling and most will tell you to test before/after water changes.
I honestly havent tested my water params of any of my tanks since they've been cycled unless a fish gets sick. ( go ahead people, flame me. Bring. It. On.)
Anyways, though it's pricy, the API test kit covers what you need to know, and will last a long while if you're only worried about the one tank.
You're dad's correct, with one betta you 'shouldn't' run into many problems, but cycling can at times be unpredictable, so the test kit is the safest way to be positive. After all, you don't want to not test, add betta, then betta gets sick and/or dies because you didn't test. So I definitely advise caution when setting things up until you're sure it's cycled. Then you can test as often as you feel comfortable.
Some medications will also cause an ammonia spike (Kanaplex is one of them...), and it's helpful to know what's going on with your tank before, and after the treatments, so you know what's going on.
I also don't test regularly, and beyond my fiance's guppies being a pain in the rumpus, a case of columnaris (because proper quarantine protocol was ignored) and a bacterial plague that has broken out once, I haven't had a sick fish in a long time.
I bought my first test kit this year, at chesh's request because she wanted to know what my nitrates were at. I also had some experiments I wanted to do that would require a test kit I don't ever test my tanks for anything, unless someone wants to know something about them. I don't even have thermometers in them since they are unheated. I am literally totally oblivious to my water parameters.
Don't get me wrong, it's a nice thing to have, especially when you are cycling a tank. But like your dad implied not totally necessary. For a betta in a 10 gallon, if you just did 1-2 water changes a week for a couple months, the tank will cycle without you ever having to test, at which point you could ease up on the water change schedule. But like I said, it's a nice thing to have and you can learn about a few things with it.
I rarely test any of my larger set-ups the tank have been up and running for a very long time get very large water changes and have been stable for tor years. My nano tanks on the other hand hand are a different set-up all together they are small planted and have a higher bio-load to water ratio that the large tank so generally I test those tank more often. A single betta in a ten gallon is going to be a very light load so you could get by without test kit it just a matter of do you want or need to know