jlk
Aquarium Advice Addict
My guess? Its really zero but compare it to distilled- if the distilled matches the spring (which matches your tank) then its reading zero. There isnt an exact explanation for this but I remember a lengthy post in respect to what is actually zero on one of my goldfish forums. Do you have any level of ammonia in your tap? It could just be trace residue from rinsing the tubes. I would not be very concerned.