Hi mandrin,
Yes, you can stir the water surface every hour or so for 5 minutes.
Or you can take a cup of water from DT and pour into sump, also at regular intervals.
If your tank temp drops too much, wrap it in towels, and fill small cold drink bottle with hot water from tap (hopefully geyser will still be warm enough?) and drop that in the tank as "warmwater bottle"
Good luck!