the slimey poop, usually an indicator of parisites. Could be undigested as you said. I'm unclear on that part, so I'll see if someone else has more insight.

As far as impaction, just had the same problem, opal ate a ton of moss. She passed a twice than normal size poop--- all moss. I added 2drops of honey per ounce (instead of 1)
And fed her wax worms, which are so fatty, when they fill up on those they get the runs. And did the 75-80 water. Depends on max temp for that species. If she basks in 80 deg-- 80 will do fine. Good luck, maybe a couple days of sun will fix her right up