My Turtle Is Sick

Question
I have a redeared sliding turtle about the size of a baseball. he is kept in about a 20-25 gallon tank. i have had him for almost 2 years now, and he has never been sick. about a month ago we bought another redeared slider, the same size from the pet shop. they were both fine.
i have no idea what happend, but the newest turtle got sick. he stoped eating, and had very few movment. his rear, and back legs sweld up really badly,there seems to be no blisters, there just puffed up. and his eyes shut. i tried to feed him several times, but he refused to. last week he passed away.. and now my other turtle is doing the same thing.
i put him on the floor today, and he was active, and i used eye drops, which opened his eyes. but by the way he was walking i can tell he is weak. and his feet seem to be swelling as well. i took him out of the tank and put him in a small one, hoping that cleaning it will help. is there any way i can save my turtle? please help. thank you.

Answer
You didn't follow the directions at all, so go see a vet. That's the only way to save this turtle now, because you aren't going to be able to buy what it needs or do what it needs if you could buy what it needs. It will be dead in a few days otherwise. It's either that, or surrender it to the local shelter that will get it treatment in time. Your purchasing of another turtle was reprehensible, when all you had to offer was a woefully inadequate tank, and likely not any filtration or UVB at all I'm guessing, because you didn't mention that. People who have the proper setup equipment tend to mention it. You had no business keeping one turtle that size in a tank so small, much less TWO of them.