I brewed a smash yesterday it came in at 1.063, I was aiming for around 1.050, is it too late to add half gal of water to my brew to equal it out? Fermentation has already started, and I don't want to risk it getting oxidized or anything.
You can do it now. If you want to be safer, you could boil (and then cool) any water that you're adding. That should boil off any chlorine and oxygen that you'd be possibly adding. Just try not to splash it in!
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you could just wait and use that extra half gallon to mix you priming sugar in. then you wouldn't have to mess with the primary at all and you'd get the same results. If you're concerned with underpitching for the gravity, go ahead and add the water now. An active fermentation will force out the oxygen from the few seconds it takes to pour in some H2O.