My 4ft shrimp planted tank have 4 new CRS female and 18 CRS new male.

Two day ago I saw the male CRS started dancing. Last night one female CRS die and this morning I found another female CRS half body being eaten. The other two female CRS went missing.

I counted 18 male CRS in the tank.

Can it be too many male CRS in the tank which result in stressing the female.

What is a good female to male ratio to keep in a tank?