My fishroom had a bathroom fan on a humidistat and a seperate fresh air intake to feed the room. I had the room set to 40% humidity. My tank wasn't running very long and after tear down I did find mold on a wall where some containers/boxes were either touching the wall or very close to it. Perhaps my fresh air vent and the fan were too close together and I wasn't getting great airflow. Perhaps this solution no matter how well setup isn't enough I can't say for sure.

This really is one of those topics that deserves a sticky as it, your health, is just as important as the rest of reefkeeping. Healthy home and body plays a role in the health of your tank; have to take care of the caretaker(s).

Since the temps dropped this week, I haven't been able to see out any windows. We need to look into something to deal with this as well.

Mold has been around for millions of years it ain't going away even though you don't see its there...i work construction and see mold in house with out fish tanks... I don't know why people freak sooo much(real money maker for me :biggrin:)..sure it has been linked too some health problems but that's why we have a immune system...i personally run dehumidifier/air purifier... IFind occasionally mold on wet windows but whip it up disinfect area a month later its there again...im not worried about it we all breath in mold spores from time too time lol

Take a trip to your local hardware store and buy a package of shrink wrap film and double sided tape. Thats what we have to use on our windows otherwise they would be so covered with condensation and ice we wouldn't be able to see out of them for 7 months of the year.

Mould is an issue in the place that I rent as well. But not necessarily because of the tank. With the tank alone the humidity in here right now is only about 40% but as soon as we boil something in the kitchen or take a shower it jumps to 60% because there are no exhaust fans in any of the bathrooms or kitchen. There is also only R 24 in the ceiling and patches in the wall with no insulation at all. Plus I've been told that this house was once used as a minor grow-op so the mould problem existed before we even moved in.

So in addition to shrink wrapping and the occasional diluted bleach cleaning we keep the furnace fan running constantly to disperse the humidity evenly throughout the house. We also keep all of the furniture an inch or so back from the exterior walls to allow air to flow behind them.

I'm journey men sheet metal worker and the best way to deal with humidity by large aquatic system is an hrv ideally put an outlet in the room the aquarium is in just like you would a bathroom and put it on a timer so it runs 6 hrs at least during the day broken up by a few time slots. 2 hrs in morning 2 in the afternoon and 2 in the evening and because it regains the heat as it changes air it won't add a lot to the heating bills in the winter

Good air circulation in your home is the key to control air quality, make sure you keep air moving and address dead air zones with circulation fans. If you can afford central air it will help with lowering humidity in your home, but keep your furnace fan running and keep that air moving.
:yo:

I find Calgary extremely dry, even now in the summer my basement where my 250 G tanks is situated the RH is only 41%, upstairs on my main level where I have a 100 G tank it's 36% on average.

I would imagine if your tank is in a 'fish room' or a smaller foot printed area then it could be a problem, I just never thought about mold due to high humidity. I would agree, air movement is critical to ensuring good air quality.

My basement windows are completely clear and I would estimate my evaporation rate is about 12-14 Gal per week judging by the size and replenishment frequency of my ATO tank.