Except member in the pool for load balance

If you have to test something, do not put that member as part of original pool.

But rather, create another pool for testing and use datagroup for whitelisting your IP, so that only you can access it.

Other should be landing to the original pool where 3 members alone are put.

when CLIENT_ACCEPTED {
    if { [class match [IP::client_addr] equals your_DGL] } { 
        pool testing_pool_name
    } else { 
        pool original_pool
    }
}