So I have a new mash tun, a 42 quart polarware with false bottom. Now my mash temps are all over the place. I mash in and am alright, within 10 minutes my temp has dropped 10 degrees, if I stir again crazy things happen. I think it may be due to too much headspace, any thought/ideas? I'm doing 5 gallon batches so my tun is only half full at most.