do you have well water? could be in the water, i would check that first

I am on a well, but i have always used r/o water in my aquarium.....oops, i think i might have topped off one time a while back with that well water about a 1/2 gallon,or so..could this be the problem? If so how can i resolve it?
Thanks, Skip

One thing to be aware of is that many of the home testing kits aren't very accurate. For any abnormal resuls, be sure to re-test. The Salifert CA test is supposed to be the most accurate, but the most difficult to use. We recently sent our water to the "Aquarium Testing Service," which is something like 100 times more accurate, and they report on 14 different tests. For us, everything was good except potassium was slightly low, and silicate and Molybdenum were elevated. It costs about $25 for all 14 tests including shipping and packaging. Something to consider periodically.
Later,
Jay