If your ammonia were 0.25 ppm and you did a 50% water change, it should have dropped to 0.125 ppm. So, I suspect that you're not reading the colours right, or the kit is off.
I suggest you retest with tap water and compare the colours ( need another tube if you're using the API kits ).
Nitrates should not rise after a water change.
Nitrites should not be 0 if your ammonia is 0.25 ppm after 6 weeks.
Dunno if anyone else here has used Seachem Stability, but looks like others here have had great success with TLC StartSmart as their bacteria in a bottle.