blood shrimp died in my 90 gallon

I bought a blood shrimp for my 90 gallon tank last week. it seemed fine..but it died today. my tanj has been running for 55 days now. the parameters are ammonia-0, nitrite-0, ;nitrate-20 ppm. ph-8.2. i have 9 fishes, 1 hermit crab, 2 BTA, 1- carpet. all are fine and healthy. the temp of my tank varies from 83.3-84.3F as its hot climate in here. i don't have a chiller yet. could anyone tell me why shrimp died ?