Welcome to JustAnswer. We are an online advice service. You are through to Dr Coles. I am a UK based vet. I am sorry to hear you are having problems with your gecko.
When did you notice this problem with your gecko? Is there an injury on the tail? Is it right on the tip of the tail or further down?
Tail rot can be due to several issues. It can sometimes be due to an environment which is too humid. Othertimes it can be related to an injury such as a bite or sometimes by whipping/whacking their tail off something.
Tail rot often requires antibiotics, anti inflammatories and pain killers. I would advise cleaning the wound very gently with dilute iodine solution twice daily. You need to be careful with this as leopard geckos can drop their tail when stressed or if it is touched/handled too much.
Otherwise I would ensure that the temperature is OK in your vivarium, check that there is nothing he could have injured himself on. You also need to check the humidity to ensure it is not too high. I would advise avoiding black crickets as they are more likely to bite.
Please do not hesitate to come back to us if you have any further questions.
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