Nitrates in my pre-mix water

[DCDeacon]

Using an RO/DI setup. Have tested and verified that RO/DI water is nitrate free. I am using a Brute trashcan that is labelled as food safe, has all the right symbols, etc (according to all the threads I can find on this topic by searching). So I don't believe there's a leaching issue, but I could be wrong. Everything I've read says I'm using the right trash can.

 

My concern is that my nitrates are a bit high in my tank and I'm trying to do regular water changes to bring them down, but I've noticed that my pre-mix water is registering as having some (10-15 ppm) nitrates. Ammonia and Nitrites don't register, just nitrates. Using Instant Ocean mix (just read the salt mix thread and might just switch to Oceanic).

 

I had been using an airstone as well as a maxi-jet 1200 for circulation and a heater. I do have a lid on, although it is not airtight. Do I need to remove the airstone as that is just introducing pollutants from outside the tank? Does having the lid on tight matter that much? I've noticed that I do have some build up on the sides of the can where the water is, almost as if I've got some bacteria growing in there.

 

I've drained it out completely and I'm going to wash out thoroughly and dry before mixing up more. Any suggestions or advice on steps or precautions to take (ie, do I need to use bleach in cleaning out the container before refilling...using proper dechlorination afterwards, obviously)?

 

Just wondering if any else has had problems with Nitrates showing up in their water and, if so, what they've done about it.