Yes I think the flatworm exit will be the best bet. When I move everything to the 5g tank from the 2.5g I will be using a new sandbed. I don't like BB tanks, so I had planned on using new sand, old sand does cause issues.
Corpusse your pico is nice, I believe mine will look nice again too when you can actually see into it
right now there's to many flatworms to see much of anything!