Postleneo - I'm to insulin dependent, never mind a pumper, so wouldn't like to speculate on these things. In any case, your experiences may differ in the Indian Ocean to somewhere less tropical.
On the upside, as you will be snorkelling, you will be close to the surface, and really only boosting deeper at your own will, should you choose to do that for as long as you can hold your breath!
If you are snorkelling off a commercial boat, they should have someone permanently on the swim platform, looking for any potential issues with their guests - almost acting as a lifeguard. Most cat swim platforms, depending on the vessel size, are either quite wide, or more frequently there are two smaller ones. You could ask whoever is on that sentry duty to care for you test kit, or reader if you are using the Libre? Obviously it makes sense to keep checking where you bloods are. Alternatively, you could decide to run a touch higher for that few hours, but that would not be my lace to talk further about.
Diving and snorkelling in tropical waters is just fab. Whether you are in deep or shallow waters, I feel confident they will have identifies spots where there will be plenty to see.
Enjoy and take care!
I think I'll tag
@Marie 2 into this, as, I think she is a diver, in warmer climes. I'm a diver in warmer climes, just not a T1!