Question: Ammonia/water levels

I know what levels are supposed to be regarding ammonia/nitrite/nitrate,my question or more quandary is that since my tank has been running,with my axies in the levels have never changed.
Every morning the results are:
Ammonia 0.5ppl
Nitrite 0
Nitrate 20
Temp is 20(I'm trying to drop it with the bottle water trick-been a bit of a heatwave this week)
Ph is in the 6's,tap water round here is very low ph
I use tetra aquasafe as a dechlorinator.
There are three little(3 inch max) axies in the tank.
Is a 4ft or 220l tank.
I'm using the api freshwater mastertest kit.
I did add tetra safestart to the tank when I started,which I know some people don't think works but after trawling the internet for two days reading reviews thought there was nothing to lose.

Also I have java moss in the tank and currently feeding the axies on bbs,bloodworms,tubifex and daphnia(not all at once,just one axie is tiny compared to others and I'm too chicken to cut earthworms up yet :s).

I thought there would be more of a spike in a level,or at least a minor change?or am I just worrying too much?!

Before I forget I do a 20% water change every day to get the ammonia back down.

Sorry it's long and thanks for any advice,even if it is "shut up and stop worrying".

Ok quick few clarifying questions
1.How long has the axolotls been in the tank? I can't tell if you've been cycling your tank for a while, or just started. I'm assuming you've been cycling for a while because of the nitrate reading, but I just wanted to be sure
2.Is that .5 ppm's of ammonia before or after the daily waterchange?
3.After the waterchange does the ammonia level go down?

The axolotls have been in the tank since Wednesday,I started cycling the tank last Sunday with someones tank media and filter pads.
The ammonia is 0.5ppm before water change and 0 after.

ah, ok well if the ammonia level is changing after the waterchange I guess that rules out chloramines, or a faulty test.
It sounds like your just on the last bit of cycling, it should eventually drop to 0 after a bit. I wouldn't be too concerned, a reading of .5 ppm's is not going to bother your axolotl much.