longest cycle ever????? Please advise!!!

[bioload]

we have been using tap water with prime as well for topping up water

This could also be the reason you have not been reading any levels of ammonia and nitrite.

"Prime® removes chlorine, chloramine and ammonia. Prime® converts ammonia into a safe, non-toxic form that is readily removed by the tank’s biofilter. Prime® may be used during tank cycling to alleviate ammonia/nitrite toxicity."