Last night I tested my water. Ammonia - no problems. Nitrites - no problems. Nitrates - no problems. pH - dropped a full point!!!
Okay, so it didn't really. I hadn't rinsed my test tube, and I guess the nitrite or nitrate test is a little acidic... I rinsed the test tube very well after that, found my normal pH, and picked my dropped stomach off the floor.
What an idiot!