You can just leave the water as-is with no worries.
As for swapping out with an airlock, that is purely a personal preference. The blow-off tube is technically an airlock, so you are really only deciding if you want to leave it alone with a large airlock or switch it for a small airlock. Either way will work.
Originally Posted by IrregularPulse
I'll make my buddy do it with me next time. That'll make me go harder at it.
"If guns don't kill people, why do we give people guns when they go to war? Why not just send the people?" - Ozzy Osbourne
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Canon T2i | EF-S 18-55mm | EF 28mm 1.8 | EF 50mm 1.8 | EF-S 55-250mm
3 whipped dog straights, Gillette Ball End Tech, 1959 Gillette Fat Boy
Secondary: Strawberry Melomel