I have two tanks, a 55 gallon well established and a 10 gallon fry tank, set up about 2 weeks in an emergency for cory fry. The tapwater in my area comes out off the charts as far as pH goes (9) but after it sits it goes down to 6.6, which is the pH my main tank is at. The nitrates, nitrites, ammonia all stay very near 0 in the 55 gallon. In the ten gallon, I've had issues with ammonia, due to the emergency set up, that I have under control with seed material and plants from the 55 gallon. I did a pH test today however, and it was too low to even register. It looked lighter than the 6.0 pH. I use the aquarium pharmaceuticals master test kit. What could cause the tank to have such a low pH? I'm freaked out. I have some zeolite in there due to the ammonia issue, and a sponge filter, but that's it. There are no meds in the tank, and I've been doing 50% water changes daily using stresscoat. I haven't done a water change since Wednesday morning however because the ammonia finally stabalized. Any ideas?