FT7 used for swimming

I got my FT7 heart rate monitor a few months ago to use for zumba. It works great for that but it did show that my heart rate might be getting very high. So I switched workouts and I would now like to use it while swimming.

I tried using it the other day and i kept getting the "check heart rate transmitter" for most of my laps and I got so distracted while trying to fix it I only did about 5 laps. I read around here that it is a common issue.

However, when trying to find a solution I keep coming across the FT1, FT2 heart rate monitors that supposedly work while swimming, and also read that it could just be the transmitter not working. Has anyone here tried to switch out the transmitter to the Polar T31C and seen a difference while swimming? I don't want to spend the money if it won't help but I do really like my heart rate monitor and don't feel the need to go buy another one if it isn't necessary.