What is the correct send and receive strings syntax for health monitoring of multiple servers in a pool ?

If you sending a monitor over port 80 a receive string of just 200 will work if the server is responding with a http 200 response. If you want to check multiple ports you could use multiple probes but each server will need to pass the health check for each of the probes! That may not work for you. If all the servers listen on port 80 and you can get the same content over port 80 that should work.