Ultra Watch not recording heart rate in salt water. How do I use Polar OH1+ with my Ultra?

My Ultra watch would store heart rate in a chlorine pool, but in the ocean/bay saltwater, it does not work at all. I've tried the band tight, snug and loose; near my wrist, away from my wrist--still no HR. I purchased a Polar OH1+ because it is designed for water. How do I get my watch to use the OH1+ for HR?