Should I ask this person for an additional recommendation?

So this summer, I’ve been working at this biology lab at a university as an unpaid internship sort of thing. I really want to ask my lab professor for a rec letter for college, but I don’t know if I should because I rarely talk to him (I’m working on a project for this postdoc at his lab). So I’m not really even sure what he could say about me besides the fact that I’m a hard and consistent worker (since I work for maybe 6 hours a day). do you think it’s worth asking him for a letter?

Who is your direct supervisor? The prof? Or the postdoc? If the latter, than get it from him. He can attest to the actual quality of your work. Otherwise all you’ll get is another generic note that waters down the strength of your other rec letters and application in general.

You don’t have to get a rec for every place you have spent time in. In this case unless you fostered relationships or personal connections that can testify to your work ethic, it might be better to just leave it as a line on your resume saying “research asst” or “biology intern” and describe what you did. That may be worth more stand alone than with a mediocre rec attached