i have water mixed 24/7/365 and every now and then it sits for that long as i have two saltwater buckets going all the time for emergencies . i would just make sure that the water looks clear and has no odor then check it with your test kit . it should be okay ,no worries . if your concerned though it may be your best option to dump it as you may have many corals or fish that it could hurt if its bad ,just weigh the odds and be smart.