Ammonia Levels?

[Kpabs]

I just posted this in my "So many questions about water changing/tank cleaning" post, but then I realized that the question I asked strayed slightly from the topic of the post. I thought I'd try it with a different title...
This is what I posted, but there's more at the end:

"Tonight did a 50% water change and did the stir and dip method (and also used a baster). I checked all my levels with a liquid tester kit and nitrite and nitrate were 0ppm, and my ammonia was up to .5ppm! I freaked, and then did lots of readings. I think (from what I can tell) I'll do 20%-30% water changes each day this week and cut back on feeding (I've been feeding him a small amount twice a day). Should I skip feeding him at all tomorrow? Is there something else I can do?"

I realize that the level isn't as high as it could be, but everything I've read says it should be 0. I got Biebs 2 weeks ago, and during that time I was still learning. I had only been doing a 50% water change once a week, and didn't know about getting all the -ahem- junk out. It's also possible that I was feeding him too much. So now that I've done the change and gotten some of the filth out, and I'll reduce the feedings to once a day, will my ammonia straighten up? Please help!

[Alex09]

Test your water straight out of the tap. It could already have ammonia before you even put it in the tank. What size is your tank/ does it have a filter/live plants/ how often do you do water changes?

[Kpabs]

That's a good idea, Alex. I'll test the tap water too. I have a 2.5gal, filtered tank with no live plants. I was only doing a 50% water change, 1 time a week. But after doing more research, I'm going to do 50% twice a week, I think...