We've solved this, although we didn't think having the addListener outside of the for would make any difference, it seems to. Here's the answer:
Create a new function with your information for the infoWindow in it:
function addInfoWindow(marker, message) {
var infoWindow = new google.maps.InfoWindow({
content: message
});
google.maps.event.addListener(marker, 'click', function () {
infoWindow.open(map, marker);
});
}
Then call the function with the array ID and the marker you want to create:
addInfoWindow(marker, hotels[i][3]);