tank cycling tanking FOREVER!!

Question
hi mike,
have been cycling my freshwater aquarium since december and i do not understand why. i did get a new filter end of december beginning of january. I understand it can take up to 8 weeks but this is getting ridiculous. I started out with corydoras 2 at a time they did ok i went through around 5 or 6 of those. It turned out that everytime i had two one died so i stopped and stayed with one i would do water changes everytime ammonia got past .5 and they died. then i decided to try a black moore (not the smartest idea but it was worth a shot it only lasted one day! now i have an oscar which is doing very well but my levels are pretty high. I have tried everything from water changes (not with the oscar i want him to live!) to amquel and ammo lock NOTHING is working and i am starting to get extremely irratated with it. does you know what i could do to maybe hurry the cycle along or why it wont finish.

the tank is 29 gallons (getting a bigger one he is only 3 inches)
ammonia-4.0
nitrite-0
nitrate-20
ph-6
thanx nikki

Answer
Nikki,
the tank is cycled but is not stable at this point.
Stop the water changes, don;t add any more fish, cut the feeding back and get rid of the ammo lock, and all that other stuff that you have used.
after 3 days or so , take those readings again.
when the ammonia hits 0 and you have nitrates, you are done.
Then get back to a regular routine of maintenance.
Do one last 20% change and monitor from there.
Let me know how it works out.