Where dd nitrates go?

[Koop]

I just finished cycle on rocks in my brute.

My nitrates where at least 80 ppm at one point and nitrites were .5 ppm.

I left for vacation for one week nd now everything shows at the bottom of the chart.

I expected zero ammonia and nitrite but nitrate??? Did the rock absorb it?

[Koop]

I guess I dont quite understand the chemistry yet.

[CStrickland]

A small amount of nitrites can fool your nitrate test into reading quite a bit higher than they are. Also, bacteria in the rocks convert nitrate to a gas, and other organisms can use it if the conditions are right. Rocks cannot absorb it.

More here, toward the bottom of the page http://www.fishchannel.com/saltwater-aquariums/aquarium-frontiers/nitrogen-cycle.aspx