Koh Nghai

Ok...so we have arrived at the charming Island of Koh Ngai, with it's dramatic interior and clean sandy beaches, the water is clear and visible...not as clear as Koh Lipe, but our main reason for stopping here was to visit the Morakot Cave 

otherwise known as the (emerald cave).So we have purchased tickets and now the girls have noticed jellyfish in the ocean, the water feels quite warmer and now we have spent the last 24 hours deciding whether or not to make the journey and 'Risking our lives' in the words of Isabella and lucie..they are chatting with the thai travel agent ,that is not helping...the red ones are ok, but the purple ones are deadly??? What would you do???