I only say caution with a yellow or blue tang because of their activity. There are some tangs that can do just fine in a 75g.
The smaller tank can stress the tang and cause all sorts of issues. Just passing on what I have learned here. I wanted one sooo bad in my four foot tank but I knew I couldnt do that to the fish, I would feel horrible if something had happened.
There are other ways to eliminate algae that are better suited to your tank.
If you are planning on upgrading within a month or two I don't think it would be an issue if you get a small one but if youre looking at next year there could be problems.
Since the tang police has been off lately I have to share what I know. Stress is your biggest worry.