Excess moisture in fish room

[daplatapus]

HRV (heat recovery ventilator). Sucks air out and preheats the fresh air coming in through a heat exchanger. No negative pressure situations which can be potentially dangerous in homes with gas fired appliances such as furnaces, hot water tank and fireplaces.
exhaust fans sucking air out of the room and pulling fresh air in is a similar setup, you just don't get the advantage of preheating that air, so in certain area's/circumstances, supplemental heating may be required.