Negative. I'll have to check it out. Rain water does most of the filling, but I do add some tap water on occasion depending how dry it's been. I'll use a little De-chlorinater and some barley extract when needed. I only feed them about every other day just in case mosquitoes take up residence. I clean the filter on the pump about once a week.
You haven't mentioned water changes yet. Just adding water to replace evaporation will lead to a buildup of nitrates over time. Not a problem in low amounts (unlike ammonia which is deadly) but in high amounts is toxic. If you aren't doing water changes, then I'm going to venture a guess that your Nitrate reading is off the scale.
That kit's cheap at any fish store.