I have that with my coffee too. I took the roots that had grown into the water out. That didn't help. And just yesterday, I watered them with coffee to lower the Ph and get more iron up in the leaves. I will see how this helps in a few days....

Living in zone 5, Coffee trees are not the easist plants to grow, but for the last 4 yrs, I've had the same plant, from a little 7" plant, to 3'.
When I repotted I used African Violet soil, a little All Purpose, Peat, handful of sand and handful of Perlite. Coffees need acidic soil. If alkaline, leaves can yellow..One to two times a year, it gets a dose of iron. I also fertilize with an acidic fertilizer. (For Acid loving plants during growing season.)
I allow soil to dry a little between watering..they don't like soggy soil. Water thoroughly, but let dry between, (if grown in a container) Overwatering can cause yellow leaves, too.
Because of dry air, it gets misted daily and a wkly shower. Coffee trees do not like hot, dry air..keep cool in winter...they love a summer outdoors..Toni