I put a dehumidifier in the fish room. Also have a large bathroom fan mounted that blows the air outside. The fan comes on with a timer, three times a day to pull humid air out and pull air in under the
door from the rest of the basement. The dehumidifier is digital and I set the desired humidity level that I want. In the summer it never shuts off. In the winter it only runs when needed. I think the humidity this morning read 35% I also run a dehumidifier in the rest of the basement during the summer. The one in the fish room runs all year. also helps heat the room. The door to the fish room stays open in the summer to keep the humidity and temp down. Of course in the winter it is open. I also heat the room that the tanks are in to 79. not the tanks. Keeps the evaporation down. Also I have glass and plexi covers to keep the moisture in. The room is insulated, walls and ceiling. The ceiling also has plastic over it to keep moisture from going into the rest of the house.
You will do major damage to the house if the moisture builds up in the framing. If your tanks are sweating, then you have too much moisture. A couple of years ago, I did not have the tanks all covered and the dehumidifier in the room and the tile near the edge of the room above the fish room peeled up off the floor. It was wet under it. Cold touching warm, humid air . Not good. My old house, I had 18 tanks in a basement. The tanks were heated and I ended up with mold on the walls upstairs behind furniture. Had to get rid of the tanks...... A heated room is the way to go.