From Tap.......

Reel McKoi wrote:
I checked the water from the tap:

Nitrates: 20
Nirites: .5
PH: 7.8


So comparing your results with the tank your tank is going through a
mini-cycle - +0.5 on what you are putting in with your tap water....the
nitrates are coming from elsewhere which would make me suspect you plant
fertilizers for starters or OTS but you appear to have eliminated that.....

I'm now wondering whether your water company is treating with
chloramines......if you have the kit test for ammonia.....I could be way
off track but failing this I would be looking at the plant ferts....

Gill