Whether you keep a freshwater or saltwater aquarium, water evaporation can cause a real problem for your tank. Not only does fish tank water evaporating make your room more humid and cause unsightly mineral stains on your aquarium glass, but the solids left behind in the water can also be toxic to your fish.
What evaporation leaves behind
Your tank's filtration system is responsible for removing nitrates and other toxins in the water due to your fishes' body waste and uneaten food. Evaporation leaves less water in your tank to dilute any ammonia left behind by the waste. That means that your fish ingests a greater toxin load at any given time.
Saltwater tanks experience a fluctuation in salinity and other dissolved elements when evaporation occurs. This is because only the fresh water evaporates, leaving minerals and salts behind. Topping off a saltwater tank daily with fresh water is essential to prevent collected salts from killing your fish, according to Salt Tank Report.
Freshwater fish tank water evaporating
Fish tank water evaporating is normal; however, there are ways to slow it down. Heat is the main cause of water evaporation, so the less heat, the better. Most freshwater fish as well as those that live naturally in shallow areas in saltwater are poikilothermic ectotherms, meaning their body adapts to fluctuations in temperature. These fish will do fine if you turn your tank heater down to the lower end of the temperature scale for their species.
Fish hailing from deep water may need a more precise temperature. As these temperatures from deep lakes and seas are usually on the cooler side, they make a good choice for a cooler tank, meaning less evaporation; however, these homeothermic ectotherms begin to flounder if the temperature isn't kept stable.
Topping off the tank is a temporary fix and one that shouldn't be relied on for more than a day or two according to FishKeepUp. It could stress your fish out and leave them gasping at the top of the tank for air as nitrate levels rise. Instead, adjust the heater and make sure it is working properly.
Fish are ectotherms, meaning they rely on their environment's temperature to be able to maintain sufficient body heat, per Environmental Science Investigation. Too much heat not only makes water evaporate faster, but it also causes your fish's metabolism to speed up, adding toxins to the tank and stressing fish out.
Keeping a fish tank cool
Besides keeping your heater well-maintained and at the low end of your fishes' temperature range, there are a few other things you can do.
- Keep your aquarium away from sunny windows and place it in a cool part of the room.
- Get a tank lid to keep evaporation to a minimum.
- If you're setting up a new tank, choose one with less surface area. The more water that is exposed to the air, the more will evaporate.
- Use low-heat lighting such as LEDs and don't leave tank lights on all the time.
- Reduce the humidity level in your home and keep the room as cool and dry as possible.
Choose a cool population
When setting up a new tank, choose inhabitants that prefer cooler waters instead of community members based on looks. Know the ideal temperature range of each tank's inhabitants and keep the temperature near the lower end of the range to prevent evaporation. For instance, common goldfish prefer temperatures between 62 and 68 degrees. However, if you live in a warm environment, you might require a water chiller during the summer months.
Fancy goldfish enjoy 68- to 74-degree water, and most tropical fish thrive at 74 to 80 degrees. That is within the range of many homes' "room temperature" and might not require much use of a heater at all. Clown loaches, discus, and rams, on the other hand, require temps in the upper 80s according to Aqueon. Expect more evaporation as your heater will run more to keep water warm enough.