How can I restore my bettas color and remove his fin rot?

[Fih]

I have had my betta for around 6 months and his color is quite dull, how can I fix it? Him tail has also started to rot and I am quite worried. Any feedback is appreciated.

The first picture is him when I got him, the second 2 are him now

 

[kansas]

I have had my betta for around 6 months and his color is quite dull, how can I fix it? Him tail has also started to rot and I am quite worried. Any feedback is appreciated.

The first picture is him when I got him, the second 2 are him now

What do you feed it? How often and how much water do you change? Do you have a filter and a heater?

 

[Dechi]

Poor water quality will do that.