Nitrate Question

[EmilyB]

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.