New Ball Problem

Hey guys I'm rather new with Balls, have only about 6months of experience.
Recently I purchased one more and the guy who sold it to me kinda disappeared. Apparently its been fed mice all its life.

My ball (he) is nearly 3ft and just over a Kilogram, but has not eaten since I got him in end Jan, tried mice of all colours, sizes and even live mice. I'm pretty sure of my husbandry since my other 2 are eating. I know it can be attributed to possibly the breeding season.
But there was this once he pooped, and it came out quite watery, I did read somewhere that it can happen when a ball goes off feed or changes food type. Is this true or does it sound more like some internal parasite that is causing him to reject food?

Thanks

Based on the watery poo, it's worth at least getting a fecal smear done.

You can also try a frozen weaned rat. Some snakes decide they like ONLY RATS or ONLY MICE, and that's that.

Hello :) First, what is the set up the snake is being kept in? Sometimes a snake stops eating because of a simple husbandry problem.