I have a 2.6 gallon Fluval Spec III. I cycled it for 2.5 months while adding bacteria culture recommended by my LFS. After my ammonia and nitrite started coming down, I planted some foxtail and sword grass. I also added a piece of driftwood. Then I cycled for 2 more weeks for a total of 3 months before testing my water again. 0 ammonia, 0 nitrite, nitrates >40ppm, and pH 6.6. My plan is to make this a RCS tank.
Anyway, once my water was good, I acquired two otocinclus* and a nerite snail at the recommendation of my LFS to get the algae under control before adding shrimp. 6 hours after adding them, 1 of the otocinclus died. The next morning, the other was dead as well
Water tests at this time showed 0 ammonia, 0.25ppm nitrite, and ~40ppm nitrate (so slight increase in nitrite and nitrate for some reason).
Then, after 4 days the nerite hadn't moved at all. I picked him up every day and sniffed him so I could take him out immediately if he died. Unfortunately, today, he smelled awful and I knew he'd died
* (I know now that this was a poor choice, but I allowed myself to be talked into it. I know now that they are schooling fish and need much more space and companions than I could provide in this tank. I have no plans to replace them.).
Am I missing something? What's going on?