Just an update. After about 36 hrs. I have Ntrates of 5ppm in my freshly mixed makeup water.

I was wondering if someone else out there can test their makeup water. I am sure there must be a few people out there who have some pre-mixed makeup water waiting to be used.

Let me know if you get the same results.

I am starting to think I am going to have to change the water the instant I make it.

Thanks.

In my case I can see how there can be some contamination back to the sw mixing tub. I use a python to drain the tanks for a wc, then I try to be religious about rinsing the hose before refilling the tanks with the new sw.

I usually leave the water in the tub cold, and just heat it before the wc. I haven't measured it for nitrates tho.

My day-old makeup water tests at zero. Same old bucket I always use. But I don't have a python...