About a week ago, I noticed a stronger than usual smell from my breeding and fry tank. This tank usually smells a bit of fish food, due to the higher feeding rates, but this time it didn't feel right.
I did a 50% water change expecting to solve the problem. No luck. I did the same the next day. The Cory's began doing more surface runs than normal. I was doing 50% changes everyday. I noticed a strange slime build-up on the glass, and a cloudy look to the water.
I continued the daily water changes, scrubbing the glass, and vacuuming the gravel. And a lot of this stuff is difficult with several floating fry traps. Anyway, after this had gone on for a week, the smell began dissipating.
And there was one last corner of the tank to vaccuum. Under the logs and stumps where the young Bristlenose hang out. So I began clearing that away, when I discovered my last remaining Apple Snail. Emphases on 'Remains'. I'd forgotten it was still in there.
The young Bristlenose' were darting in and out of the shell, so I guess they were helping me clean up. Overall, I only lost 1 juvenile Cory, who came down ill during that time.