Sick Guppies

I had a tank of 8 guppies. Over the past 3 days, two have died. The second one clamped his fins, and then the second half of his body became bent down. Now a third fish is starting to look the same way. What do I do? Ive tried salt and melacure the past two days, but he looks worse. First pic is the current one, the second is my guppy that passed away.