Slow R/O unit water production

[Coralgurl]

What would cause an R/O unit to slow water production? I have a 100 gl/day RO unit (Vertex), and lately it is taking forever to produce 30 gls of water. By forever I mean I ran the unit from 4 pm yesterday afternoon and at 8:30 this morning I had maybe 15 gls of water. My membrane was changed a year ago and the filters 9 months ago. My TDS meter reads 0 so no reason to change anything. The unit is approx. 2 1/2 years old.

Previously, I'd run the water from 9 pm and by 7 am, I was close to overfilling the 30 gl container. I typically don't touch the unit and run it once a week, depending on outside temps. Length of time running depends on whether I've done a water change or not (fill one or two containers).