About a month ago I did a water change. Before the water change, the ammonia and nitrites were 0ppm, and the nitrates were, if I recall, a bit high, 5 ppm maybe? The pH was 6.8. This tank has been established for quite awhile, since April or so of this year. Up until the water change, there had been no deaths or illness for months and months.
The day after the water changed I noticed 3 of my 5 guppies were missing. I thought they were dead, but 2 of them came out of hiding and were acting super strange. Hovering near the bottom of the tank and shimmying.
3 days later, one of the missing guppies returned. The other two died behind the driftwood somewhere. Initially, I only thought the guppies had been affected, but I noticed my corydoras habrosus had taken a hit as well, with several of them having disappeared.
The water was conditioned before putting it in and it felt like the right temperature although I did not check. Nothing really was done out of the normal compared to all of the other water changes I've done.
The next week, I did another water change and ALL of the guppies disappeared for a day, and all eventually reappeared the next day.
Now, it's water change time tomorrow and afraid to do it! I -think- the water change that started all of this was done with a new dechlorinator than I had previously used. Could that have done it? Perhaps I didn't let it mix in well enough or something?
Does anyone have any idea what I can do tomorrow to prevent more fish from dying during my water change? Thanks in advance, hope you guys have some ideas!