I have a 10 gal. at work that has been up and running for almost a year now. A few weeks ago, I started increasing maintenance for fear of OTS. I gravel vaccumed the 1/2 in. substrate, and pulled a massive amount of gunk. I then took the filter floss out of my whisper 20 filter, and thoroughly rinsed it out in tap water. That thing was nasty. Of course, I have a secondary foam element, specifically for nitrifying bacteria. That one I didn't touch. I removed 4 gallons during that cleaning, and refilled with tap water that was left sitting in my cubicle the day before. At this point, my tank conditions were fine, 0 nitrite, 40+ nitrate (oops), no ammonia test, I took that one home.
I come in the next day, only to find the angelfish belly up. My coworker wasn't too happy about that. Not only that, but the water was beginning to cloud up. I tested the water and was surprised to find 3+ nitrite. Yikes. Fortunately only the angelfish were the casualities. I have since done 40% water changes every 2 days to get the nitrites down, I think washing the filter floss killed the cycle, and my tank is going through another cycle.
I come in the next day, only to find the angelfish belly up. My coworker wasn't too happy about that. Not only that, but the water was beginning to cloud up. I tested the water and was surprised to find 3+ nitrite. Yikes. Fortunately only the angelfish were the casualities. I have since done 40% water changes every 2 days to get the nitrites down, I think washing the filter floss killed the cycle, and my tank is going through another cycle.