ah I knew it that I shouldn't have eaten all that jelly. How many do you need for the quest? Just so that I can save them up... and then eat the rest. :D
Thank you for sharing your impressions, I didn't find anything behind the balloon aside from rocks and branches but it gave me strong "hidden stuff" feelings so I'm happy you found your treasure!
You need three!! One of each (sea, river, and cave jelly) to craft the fish smoker, to
then complete the quest. I actually got the first cave jelly from my lava eel pond, and apparently, you can get ocean jelly from flounder ponds. I just fished for the last two though, it only took one in-game day with +2 luck but it's not much! ^^;
You need to actually
catch all three with a fishing rod though to complete your compendium, so I'm about to go back into the cave for more!
Also thank you!! About the balloon thing. Maybe they show up in random locations? No clue but it's worth looking around. :)