How Often should you test a 10 gallon tropical fish aquarium to check if it has the proper chemicals?

I just got a 10 gallon fish tank. I have a heater, a bottom dweller, and not the best quality filter that I have to change once a week. I don't mind changing the filter once a week and it was a lot less expensive than the filter that you change once a month. Anyway today I just bought a water test kit to check the PH levels and so forth, it did not specify on the package about how often you check the water. Today it said the the levels of chemicals were fine. Also how often should I change the water, I am aware that every time you change the water or put more water in you have to put the stress reliever conditioner in which I have. I hope I am on the right track with these fish because It is a lot of work! If you could help me that would be great thank you