Both readings were taken just at the surface on opposite ends of a 33L. I did add the powerhead a little bit ago, but haven't taken any additional readings yet, as I had to feed the kids and clean up the "school is out for the weekend, lets trash the house" rampage through my house. There also seems to be a new oil slick looking mess floating on top of the tank water that I am not too happy about. It is time for a water change tonight I think.
Jan
Jan