Where are these nitrates coming from?

[Bugeater281]

So if I test my rodi(at zero tds). There is no nitrates. But after mixing fresh saltwater, if it sits for more than 2-3 days. It’s sitting between 2-10 ppm of nitrates. I’m already fighting two systems that run around 50ppm+ yet I can’t keep any phosphates in my tanks. I’ve started dosing phosphates. And I’m still doing water changes(10ppm is better than 50ppm).
Here my concerns, I’ve cleaned the water mixing barrel and equipment. And it still happens. It could be because I don’t usually have a lid on it. But I also suspected that some chloramines may be getting through my 5stg rodi system. 220ppm-10-14ppm after ro, and zero after di. However I was under the impression that chloromines turn to ammonia. But two days doesn’t seem like it would be enough time for bacteria to convert the nitrogen cycle. Another option is maybe the barrel is leaching them.
I’m posting here to see if anyone has ideas. Or has had a similar situation. I was using tropic Marin, I just bought some hw-marine. Since tropic always out of stock. But I kinda doubt that the nitrates are coming from the salt.

 

[Ryan3313]

Put some of your rodi in a different container and let it set a couple days and measure nitrates to see if it's your water. Mix a small batch of salt with distilled water in a different container to see if it's the salt. If the small batch of rodi and the small batch of salt mix both have no nitrates then maybe it's the container.

 

[Cory]

New saltwater could contain enough ammonia that when bacteria convert it produces readable no3