[pollywog]

It could well be a bacterial infection, Chinese newts are quite commonly affected by bacterial infections that cause ulcers or eat away at limbs. It's possible they've been harbouring an infection since you've had them and a change in conditions has bought it on. The good news is if you can stop it the missing bits should grow back, best thing to do is get a vet to swab it and see if he can give you a treatment. In the mean time keep them clean and cool them down slightly to slow the metabolism of the newts and the infection.