Nitrate Question

[Chad]

Ok,

So, my tank nitrates are at 30 - 35 or so.. I decided to test all 3 steps to the tank.

Tap: 0 ppm
RO/DI: 0 ppm
Make Up Water (Kent Salt Added): 10 ppm

Now the part that makes no sense to me is the make up water. I am wondering if this has to do with the fact it was sitting in my mixing pail for about 3 days (circulating and heated of course). Does anyone have experience with this? I never bothered to measure the make up water before. Not thinking it would change. Any chance it could be introduced by the salt mix?

Thanks for the help..