help! my new turtle has a runny tummy :(

[Turtle_Crazy]

Yesterday, while feeding my turts in the feeding rubbermaid, my little one, Soup took a solid #2 then had a very wet #2, so i changed the water, keeping it very close to the temp it was and then she had another wet one again. this has been going on all yesterday and some of lastnite. ive been changing the water everytime and their diet this past week has been as follows : most to littlest amounts:
-spring mix
-romaine
-endive: ^---all three available most times
-defrosted mixed veggies
-spirulina pellets
-a strawberry coated in rep-cal every three days
-chopped papaya, and cantelope
-feeder guppies
-a mixture of reptomin/mazuri/wardley/gammarus pellets

im thinking it may be the mixed veggies, do i need to cook these before i offer them? (feels bad)
Should i quarantine the little one?, the big girl is having solid ones still.

Thanks for helping:dumb:

Nicole