If you are testing, and you notice that the ammonia or nitrite levels get up into stress out or kill the fish territory, you can do what I did and take Fusion out and put him in a little bowl you can easily clean frequently until his tank settles back down to levels that won't hurt him.
True, my overfeeding caused a problem with my small tank, but you never know when something is going to go wonky.
All I'm saying is that if the fish seems stressed, sick, or off somehow, I'd get him out of a situation where he's constantly exposed to ammonia and nitrite without clearing out the progress you've made in the tank so far.
JKFish- I have a new 5 gallon tank. I just put my new fish into it yesterday. Until I can source the test kit you suggested how often and should I change out the water? I would prefer to not do a 100% change also.
blake: You can get the API MAster Test kit at Petsmart, PetCo, or any pet store that sells fish. Or you could get it online if you want to get it cheaper and wait. Just make sure you get the Fresh Water test kit and not the Marine test kit.
As for how often to change it without a test kit I'd wait for JK's answer. =] I have no idea on that one. Just thought I'd answer what I could. =]
In my uncycled 5 gallon, I did one 100% change weekly, on top of a 25% one.
If you're cycling with fish in your tank, like I did, be sure to stay on top of those water changes! Sometimes I had to do more than one water change a day to prevent the ammonia from going up too high. Keep a close eye on the levels.
I've read through the stuck thread about cycling, but this is really helpful to have it broken down to really basic. I'm nervous about doing this but I think I do want to do the cycled tank too. Thanks!
Blake: Kfish and Jupiter are right. Do about two 50% water changes a week with one being a gravel vaccuum as well would do, though if you see your betta acting oddly, do a 25-50% water change. Make sure you remove uneaten food. Once you get your test kit, you'd probably want to test daily and do water changes as you see the ammonia or nitrite get too high (above .25 ppm) (sorry for the late reply D: )
CanuckFins: What I described was with fish in, fishless has slightly different instructions. I'm glad it helped ^-^