If you have been doing water changes like that for the entire time you had your set-up you have essentially been removing the nutrients to feed the beneficial bacteria. During cycling, I have purposefully not done any water changes for at least a month or two then only a small one. Once the ammonia has reduced to low levels and the parameters are not changing I then would wait a little longer then perform a 100% water change and be done. Chances are that your tank is in stasis at this point and you have actually completed your cycle. There are sufficient bacterial colonies to handle the livestock you have. Still, 40 - 50% seems like a lot.Alright . I was doiong a waterchange just in case. Every 3 weeks the tank usually still looks perfect . But I just did them to be on the safe side .