okay now I'm really confused. Isn't almost all of the benifcial bacteria in the substrate and filter (my UV unit is after the filter)? I was under the impression that the amount of bacteria in the water itself is pretty small.With UV, one specific danger is uncycling the tank. I had two serious episodes like this, in both UV fully eliminated the nitrite processing bacteria. In one case, I had to fully empty and wash the tank before I could restart the cycle.
Batch