Has it been in the same pot and soil since you got it? The soil looks old and dense to me.

I'm sure someone with more knowledge will have answers for you..

It really needs to be in a larger pot. The newer leaves look healthy so the stress that caused the older yellowing leaves has passed, and it was most likely too much water without letting the soil dry out a bit in between waterings.

Each new leaf emerges green, but begins to yellow as the next one forms - can't seem to sustain green leaves. I will try to hold back on the watering.

It should probably be re potted before the winter.