HELP! Corydoras spinning in corkscrews

[MeatGoesHam]

Hello guys I really need your help. 10gal with buffer, 4 corys
(2 spotted/peppered 2 Julie) 2 Amano shrimp
gh:~80 KH:~150 ph:7-7.5 NO2: 0ppm NO3:0 ppm ammonia:0.1
Using water drop test for ammonia all others are through test strip which i did x2
I came home the other day to find one Julie corydora dead on the bottom of the tank, and another cory(Peppered) swimming in corkscrews landing upside down with heavy breathing. I ended up euthanizing that one because he could not move at all without corkscrewing. Now today I find my last Julie cory corkscrewing around the tank landing upside down but after a small rest went right back to swimming normally.(5 min ago) I have no idea what is wrong plz help! I'm performing a water change and tank clean right now to lower the ammonia.
Thanks to anyone who can offer up some advice

 

[MapleNeil]

Hello guys I really need your help. 10gal with buffer, 4 corys
(2 spotted/peppered 2 Julie) 2 Amano shrimp
gh:~80 KH:~150 ph:7-7.5 NO2: 0ppm NO3:0 ppm ammonia:0.1
Using water drop test for ammonia all others are through test strip which i did x2
I came home the other day to find one Julie corydora dead on the bottom of the tank, and another cory(Peppered) swimming in corkscrews landing upside down with heavy breathing. I ended up euthanizing that one because he could not move at all without corkscrewing. Now today I find my last Julie cory corkscrewing around the tank landing upside down but after a small rest went right back to swimming normally.(5 min ago) I have no idea what is wrong plz help! I'm performing a water change and tank clean right now to lower the ammonia.
Thanks to anyone who can offer up some advice

What other fish do you have in the tank? Did you make any changes to the tank recently? How long has it been established?

Edit: I recently lost 4 of my julii cory's in a similar situation. It may have been from stirring up the sand, or possibly they felt threatened because of a new fish I added, and my theory is that they used their neurotoxin because they felt threatened and it affected the others in the group. 2 of the 6 are doing fine again, after I removed the survivors from the tank for a while to recover then put them back and they are doing fine.

 

[MeatGoesHam]

What other fish do you have in the tank? Did you make any changes to the tank recently? How long has it been established?

Edit: I recently lost 4 of my julii cory's in a similar situation. It may have been from stirring up the sand, or possibly they felt threatened because of a new fish I added, and my theory is that they used their neurotoxin because they felt threatened and it affected the others in the group. 2 of the 6 are doing fine again, after I removed the survivors from the tank for a while to recover then put them back and they are doing fine.

This tank has been established for 6+ months now and i have lots of algae markers and water bears to signal a healthy environment. No other fish have been added and thats the entire population of the tank at the top of the original post. I seriously have no idea what happened and I feel like the remaining corys are quite depressed after losing their friends. I don't wanna lose anymore and I haven't been home today so I fear one may have already passed. Thanks for your help