Originally Posted by scottyspohn
Can I add another gallon of cider to it maybe sweeten it up a little and how much apple concentrate do I add I know everyones taste is different but what is commonly used for a 5 gallon batch
I would hold off on the concentrate at his time, add that when bottling.
If you add cider to take up the headspace, that will probably start up a secondary fermentation. This is not necessarily a bad thing.
Some people use sanitized marbles to take up the headspace without restarting fermentation.