Hi Mike, Chris is correct, his method does work.
I raise matas in a bare tank with pieces of driftwood for decoration & acidity.
You need a lot of biological filtration to keep nitrate levels low. You can use a combo of a sponge filter with a Whisper power filter stuffed with a lot of foam bio media.
Change 25% of the water twice a week or whenever you see poop.
A small amount of plain, non-iodized salt helps prevent fungal growth in soft-shell turtles, but it may help matas too.
To treat, I use Betadine on the wounds, and gently debride off infected cheesy parts of the shell with a cotton swab. Let iodine air dry for 1-2 hours, therefore turtle needs to be dry-docked in warm room. I use peroxide as well to disinfect too.
Water pH is around 6.0 (SeaChem DiscusBuffer or AcidBuffer)
Good luck,
Minh
16 matamatas owned over 11 yrs (6 died of parasites/bacterial inftns of skin/shell)
714-750-4201
Calif.