You can log your outputs an add verbosity e.g.
#!/bin/bash
while read p; do
echo "try $p"
echo "\x00\x00\x00\x00\x00\x01\x5A\x30\x30\x02\x41\x41\x1B\x22\x61 Test message!\x04" | nc -v "$p" 3001 2>&1 | tee "$p.log" &
done < candidateIPs
wait
You can examine either the ip-specific log files after that.