coolwaters : yes there is die-off...but the rock doesn't smell so bad. I've put 50% of the rock in the sump, after a powerhead/toothbrush clean of what could have been rotting outside. I already have 130 pounds of rock and there is no noticeable ammonia.. in a 113g of water ..just to be cautious i added a polyfilter pad to remove all sort of crap...plus it changes color if there is ammonia. So..the 2 damsels are in the tank, but the whole thing isn't really cycling. For that low % of new rock it's safe.