Is there to much headspace?

I want to use a Spiedel 15.9 Gallon tank as my fermenter for a 5 gal. batch of All-Grain. Is this to much head space for a primary? FWIW I did use this previously and the airlock showed plenty of activity so I assume it will be ok, but I’d like to be sure. So I’ll tap into the knowledge here :cheers:
I’m not so sure about using it as a secondary. I’ve seen posts about doing a Co2 to purge at that stage, but the secondary is not so much of a problem to clean for me. When I do move to 10 gallon batches I will be using it then
thanks!

                     FoamFollower

Ever hear of “open fermentation”? That is the way many beers were traditionally brewed, and the head space is essentially the entire brewery. No problem for you. If you want to age the beer in bulk for a long time (more than 3-4 weeks), you might want to rack it to a container without any headspace, but otherwise you can ferment in the tank and then just rack when you put it in your bottling bucket.

Thank you rebuiltcellars

Completely off topic— My brother married into a Finnish/American family in the U.P. of Michigan (where I grew up) and he has in-laws named Inannin, and another named Outannin. I may have misspelled them. I sure laughed when I saw the wedding registry
There is a very large contingent of Finnish descendants up there.