Shrimp dying and I don’t know why

My neo red cherry shrimp that I have bred and had for almost a year are dying one after another. I have lost about 20 over the last 4 days. The two in this picture have the “ring of death” but not all of them have had that and surely failed molting isn’t contagious right?? Adults and juveniles are dying, no growths or signs of infection, water parameters are perfect 0-ammonia, 0-nitrite, 5-nitrate, temp is 76 (I know it’s a bit on the high end but that’s what I’ve always had them at), sponge filter with bubbler. I have never lost shrimp like this before. If the adults were dying out after aging would be one thing but the young shrimp are dying too. How do I save my colony?? I don’t see any parasites but could it be something microscopic? Recommended treatments? I’ll be putting in almond leaves today.

My neo red cherry shrimp that I have bred and had for almost a year are dying one after another. I have lost about 20 over the last 4 days. The two in this picture have the “ring of death” but not all of them have had that and surely failed molting isn’t contagious right?? Adults and juveniles are dying, no growths or signs of infection, water parameters are perfect 0-ammonia, 0-nitrite, 5-nitrate, temp is 76 (I know it’s a bit on the high end but that’s what I’ve always had them at), sponge filter with bubbler. I have never lost shrimp like this before. If the adults were dying out after aging would be one thing but the young shrimp are dying too. How do I save my colony?? I don’t see any parasites but could it be something microscopic? Recommended treatments? I’ll be putting in almond leaves today.