my tap water, i tested it with the test strips, that i also use to test the tank water. the tap water is as close to what i get a reading on when i test the tank water, but i do use a de-chlorinator as well, as i also set aside 3 gallons of tap water, in jugs for changes. my nitrite level was high, so i did a 25% water change, and added the API salt, which i had on hand. i can test the tank water again, later today, or tonight, as i want at least 24 hours of cycling.. i also (per directions of the filter's maker) replaced the charcoal bag, as it was nearing the end of it's use (one month) in 2 weeks, the foam filter gets replaced. and in about another month from now, the bio beads bag gets replaced.