these would be the ones you just got the other day?
poor diet and lack of uv light would be my first guess.get some decent food and get them into natural sunlight if you can,other than that a good new uv light tube as low down over their basking area as you can.Feed them calcium rich foods such as small fish with bones(guppies,culled goldfish etc)stay away from red meat,oxheart as even though you can dust it with calcium it will wash off in the water.Processed turtle foods with the calcium added will be better,also float a bird cuttlefish in there,they will gnaw on it to get calcium.