Ghasts spawn way to much its been happening alot and i cant hardly go to survival

Put the summary of the bug you're having here

What I expected to happen was...:
there to not be ten Ghasts at one time 

What actually happened was...:
about 7 to ten ghasts at one time where appearing 

Steps to Reproduce:
1. go to soul sand valley 
2. ... wait for ghasts to appear 
3. ... count the ghasts