Went back to Perplexing Pool today, and drained a large area of the level. This also provided access to another dungeon, which I went on to complete. There was a boss at the end (as usual) who was tricky to kill (again) until the method of doing so was found. That he was easy. After that, I wandered around Perplexing Pool for a bit, and then got attacked by loads of huge baddies (including the giant spider thing from another cave which just appeared from nowhere) and lost about 40 Pikmin to them. Found a bit of treasure, and rebuilt my Pikmin army then. Up to 78% debt repaid now.