Blood huting: Am I doing something wrong?

[Cheezeninja]

Im playing a huge mictlan game right now (on the Faerun map) where i have about 20 provinces set up for bloodhunt/sacrifice, i figure if im going to build a temple for sacrificing, and a lab for pooling blood slaves, i might as well put in a watchtower as well. I pull around 300 blood slaves per turn (i have 2 priests with SDR's in every blood hunting province, and 1 sacrificing) but im also slowly killing off my population. As long as i keep expanding i'll be fine, the blood must flow, right?

I have growth 2 and most provinces have a king with 50 slaves patrolling.

Its on the Faerun map, which is a pretty hefty download if you dont have high speed internet, but i can send you the save file if you want, so you can get the idea of what a semi-massive blood empire feels like.