Very specific question about rotten egg smell and discoloration (slime ?)

I change the water for my marimo once every 2 weeks, and squeeze the marimo out of the old water once every week . Whenever I squeeze the water out of him, the foul smell hits. His jar smells like nothing, he when dry doesnt smell , and when I put new water in him to clean him, he doesnt smell . It's like the water inside him stinks, but once I squeeze it out the smell is gone and doesn't return for a few days . Is this fine or is he possibly hurting from the inside ?

I've also noticed since I got him these small patches of brown hairs that are clumped a bit together and I'm not good at taking it off, whenever i scratch it it doesn't come off and filling him up and squeezing over and over doesn't clean it . I don't know if it's slime or not . It's more noticeable in person and ive put a filter over the first photo to show what color it is closer in life . Any ideas on how to remove or if it needs to be removed at all ?

He gets a few hours of indirect sunlight from outside (I live in UK so maybe 5 hours of it and also quite dim), 19⁰ water ,fluctuates to 18 or 20⁰ , and his water in the jar has never stank like rot. Photo 2 and 3 have no filter

Thanks in advance !