Hi, new here to the forum as well, but not new to the hobby.
Buy yourself a good water testing kit. Testing your water is very important for the health of your fish.
API Freshwater Master Kit has worked great for me.
When testing for your Nitrates though, be very careful to follow their instructions. Also, NO3
bottle #2, when first using it, tap it on a hard surface, breaking up the components that do get stuck to the bottom of the bottle, for about a minute, then shake vigorously for another minute. They do have reports of false readings due to the issue with bottle #2.