Hes missing entire chunks of his head which would be the worst case of hith I've ever seen. Search in the disease section as I had a rhom with hith and had a number of threads. Best treatment is metro+ and Epsom salt but it needs to be ingested consistently and at the right dosage. HEX by nls is also suppose to be very good. High quality water would also go a long way. Do you have soft water? The bacteria that causes hith thrives in hard water but not soft water.
Post pics in the disease sections as some of the folks there are experts on hith.