Ok so, I get the "it's a never ending struggle" with these little guys. I am unfamiliar with your tail issue but my axolotl, I've noticed that it's hard for me to judge her coloring against her deep brown sand. When I tubbed her today cuz I thought she had some fungus, she puffed up and stood her ground against me and her gills got super flush with blood and what I thought was fungus, was just a tired axolotl. Then after her fridge trip, she was happy so I put her back into her tank.
Have you seen anything that might explain the red specks on the tail? How old is he? It could be some natural coloration but don't hold me to that. See if one of the more experienced owners knows. My axolotl started to get black spots on her feet and underbelly and everyone said that's just her maturing and aging. But he's are black spots, these reddish ones, I don't know man.