I wasn't sure if I should post this in the illness forum, since it specifically states that it is for betta illnesses.
In the last 5 months or so, I have had 4 snails (3 mystery and 1 nerite, never more than 2 snails at a time live in the tank, and I got the second pair after both of the first pair had died) live with my betta, a hyper HMPK. All of the snails have died, and my betta appears to be healthy as a horse -- and he is NOT killing the snails. He barely knows they exist, and when he does finally see them, he stares for a few seconds, then swims off to go investigate his reflection. I have watched this for many hours at a time, and the snails are not being eaten. They die in their shells, and I verify death by smell (and oh my is that a bad smell)
Water parameters (tested with API liquid tests) always show 0 for Ammonia, Nitrate, Nitrite (sometimes just a hint of ammonia (like not even 0.25), since I do my water testing with water changes (i.e., I test a cupful of the old water). Tank is kept at 81 degrees, 5 gallon heated with sponge filter, load of live anubias, wisteria, and java fern plants, bare-bottom. I drop a drop of Flourish in about once per week, and I make sure the snails are near the bottom of the tank before I add it). There are a few clean shells in the tank and some cuttlebone for calcium, and I drop fragments of OO veggie-algae wafers and some bits of extra OO or NLS pellets for them. Obviously, the nerite ate algae, and was the biggest pooper ever to grace a tank.
The nerite (Batu Khan, maybe 1 cm across) died after about a month. His tankmate Nokhai Khan (golden mystery snail, about an inch across) died after about 3 months. Ogedei Khan (wild-type mystery snail, about 0.5 inches across) died after 6 weeks. Chaggedei Khan (golden mystery snail, started out at 0.5 inches across and doubled to at least an inch after 1 month), died after 10 weeks.
All this time, the betta had been well and does NOT harass or eat the snails -- he's not the brightest fish, and I think he forgets they are there most of the time) The nerite was shut tight in his shell when he died, and had been for about 5 days. The mystery snails were in typical dead snail position, slightly open. 3 of the 4 snails died about a week after moving, but seemed happy enough right after the move. All 4 seemed to be relatively closed up for most of a week prior to death.
The only other clue is that the golden snails developed a brownish color on the shell which seemed to get more pronounced and the snail got a bit less active with time. I have attached a photo of Chaggedei about 10 days before his death.
All snails were bought at Petsmart -- the first two from the same place I got the betta, and the last two from a different Petsmart (but both from the same store).
Does anybody know what is killing my snails? This is getting very depressing! Perhaps they are just old (I know warmer water makes them more active but die faster)? Are Petsmart Snails usually short-lived? Am I doing something wrong?