Dehumidifier in a Fish Room

[Myka]

Do you have central AC? Or a high efficiency furnace that you could leave the fan on all the time without costing a fortune?

Either option will produce positive air pressure in the room provided you make sure the room is sealed well (check the door in particular, maybe lay a towel on the floor to block the air under the door). Then drill a 1" hole in the wall to the outside at floor level, shove a 1" PVC pipe in there and put mesh on the end so that bugs don't get in. Humid air sinks, the positive air pressure will push air out the vent. No additional electricity used.

An HRV is the best long-term option though.