Chris, I never had a Ninja, but I often replaced pumps on various other machines , sometimes after six months or maybe even less. I started doing two things and have never replaced a pump since then.
No. 1 . I never use powders in my solution tank anymore, just plain water.
No 2. I only fill with hot water from the household tap and then use an in line heater if necessary to heat the water further.
I have found that by doing those two things it will prolong pump life considerably.