High nitrates in new aquarium?

[awexis]

I'm new to this site. I created an account just to get some opinions and help on this problem I'm having. So I converted my freshwater aquarium to a saltwater aquarium two weeks ago. I have a 29g biocube. I added 30lbs of live rock and 10lbs of live sand (I was hoping to add more sand eventually). The rock was fully cured and came from a friend's tank that they were breaking down. I just bought caribsea live sand from Petco for those 10lbs. All the water was purchased from Petco so my tap water would have no effect on the nitrate level. All that is currently in the tank is a few tiny snails and hermit crabs. Not a huge bioload at all. Ammonia tested zero and so did nitrites but the nitrates were through the roof today. Usually this is seen in old aquariums that have been neglected on water changes and such. I'm confused as to why this happened. I was planning on doing a huge water change, but I don't think that will help in the long run. Any suggestions or ideas as to why this happened?

[JWClark]

Even if the liverock was cured, moving to a new system will cause some die-off (out of the water while transferring and, more importantly, stuck in another tank w/ different parameters). This die off is likely where the nitrates came from. Also, could have a large amount of detritus w/in the live rock depending on age and placement in the previous aquarium.

Do your water changes and give the tank time to stabilize.

[bertoni]

I agree that the nitrate is likely from debris or die-off. I wouldn't worry much. Some water changes will speed the process of removing the nitrate. For whatever reason, our tanks generally are better at converting ammonia to nitrate than they are at reducing nitrate to nitrogen gas.