Aquariums: My bettas fins are turning see through

Does anyone have any idea why this might be happening? I see slight fin rot on the top fins on his back but I’ve gone through the process of changing the water and keeping it clean… nothing else seems to be frayed but he’s losing colors in his fins. He has been changing many colors within the last few months but I don’t think see through us normal? (The first pic is now, second is about a month ago.)