I just lost two sens a day apart for no apparent reasons. African Knife and the Cherry Barb That Will Not Die Or Get Eaten are fine. Ammonia 0, nitrite 0, nitrate was a tad high when the first one died at 25 ppm, so I did a 30%, 2nd one died the next day. Neither displayed any signs of distress before dying either, they were eating well and everything. No gravel to swallow, it's a sand bottom. I'm baffled. Really annoyed, too, fish don't normally die for no reason if you've had them more than a week or two and these boys were coming up on 6 months.