Sounds like a bacterial bloom. Was that tank cycled before you put the fish in? Keep a close watch on your water parameters, and if you have any ammonia or nitrites, do a water change. Otos are very sensitive to less than perfect water conditions.
What's the temperature of the tank? You really need ammonia, nitrite, and nitrate test kits to know what's going on in your tank. You can get the Aquarium Pharmaceuticals Master Test kit which contains all 3 tests plus ph tests for under $15.00 online.
The snail heaving is his breathing. It scared me too the first time I saw it. That "feeler" is his breathing tube and he puts it through the surface to get air. They don't have to do it very often. I guess that is why it is so scary.
84 degrees is however too warm for either the snail or the Otos. You can lower the temperature by changing 50% of the water and using cooler water and setting the heater way down. (like at 68 degrees) It is always a good idea to at least do a major water change when a fish has died in a tank and wipe down the walls on the inside. You could even change 75% of the water if you feel the dead fish may have had a factor in this. This is what I did when Noel died and then ran Melafix for a week to cut any bacteria that may have been left in the tank.
Gunnie is right though. You really need to know the parameters of the water, especially ammonia, nitrites, and nitrates. Otos do not take kindly to water that is out of limits. The snail is more hardy but will not take water that is way off base.
I don't mean to scare you, but I am saying this out of personal experience: poor water quality, or even just ok water quality that is fine for the other fish, is bad news for Otos...like they could come down with severe finrot and that is no fun at all for either party, trust me. Get that test kit and make sure your water quality is really good--aI'm for nitrates of 10 and under, if possible.
0morrokh if I wanted to get 2 oto's, my nitrate is at 20 no matter what I do. I have some live plants in there, 11 now, but wonder if I should research plants that will use the nitrates the most and wait to see if I can get nitrates down to 10 before considering the otos?
The otos will be fine. I know the RECOMMENDED level is 10 or lower but my little guys have never had fin rot and they live in nitrates that are between 10 and 20 most of the time and they have been as high as 40 when the water was bad and I could not get out to get spring water. (NOT for long but it did not kill them) It will make a difference when you put plants in the tank and all plants use nitrates. I have wide leaved plants in my tanks because I find that they do better and I think the fish like them better and the extra surface area makes for more photosynthesis. (plus I think they are prettier )
TY Rose..and one more question regarding live plants? I can buy a really cheap C02 setup for them (for $20). I know it'll sure help the plants but what about Zen and other fish? Do you know anything about CO2 and whether it is harmful at all? It's probably not since so many use it but want to be sure there aren't things about using it I should be aware of.
I'm going to do internet research on that too so if you don't know off the top of your head, pls. don't take time to find out for me. You have enough to do I'm sure!
Edited to say that I'll take this plant question over to the sister plant forum...where it belongs, heh. Sorry.