Glad your nitrate problems are sorted and your molly's doing ok. Just curious now - what plec have you got? If he's an ordinary "garden variety" plec, your tank is way too small for him. They can grow to well over a foot in length (mine's about 2.5 years old and he's about 8-9 inches) Also, with the amount of fish in your 10 gallon, you should do more frequent gravel cleans. Plecs are poop machines, and this could be why your nitrate levels are so high. Try doing a light gravel clean once a week and see if that helps keep the nitrate level down.