At this stage, it seems that the rust at the bottom of the fuel tank does not require treatment. However, I’ve noticed that it has spread over the past four months. I have been using 91 octane petrol and keeping the fuel tank completely full during this time. Should I treat the rust now to prevent it from spreading further?

The photos are from four months ago and yesterday, respectively.

Just picked these up in the last month. 1998 ATK 250 LQ and a 1973 Honda XR75.

The 250 and the XR75 are really clean. The XR75 I used to ride as a kid.