Water evaporation is a battle that every hobbyist will encounter. And to top that off, evaporation rates will be inconsistent from one aquarist to the next. This will be dependent on where you live, elevation, weather, season, and indoor atmospheric conditions. There is no stopping evaporation but there is slowing it down. Below will be some general tips and discussions about evaporation, how to slow the rate, and how to properly replace evaporated water from your aquarium.
What should I do about water evaporation in a freshwater aquarium?
As mentioned before water evaporation is going to be a concern when owning an aquarium. When water evaporates from a freshwater aquarium you must replace it. The important thing to remember is that you must not just replace it with regular tap water. This tap water must be conditioned with some type of dechlorinator. One of the main concerns of water evaporation in a freshwater aquarium is letting the pumps run dry. This will be true for hang-on the backs, canisters and sumps. If the water level gets too low the pumps will pull air and sease to work leaving your tank without a filter and without water movement. This can ultimately lead to the fate of your aquatic animals. Be sure to always have water ready to go whether it is in a milk jug or a remote reservoir. This should be kept in a covered and safe container at the same temperature as the aquarium.
As a preventative measure, You should alway consider covering your aquarium with a lid. The Glass/plastic/acrylic lid or top may not totally stop water evaporation but it will help slow the rate. You may notice condensation on the lid - this will be a clear indication that the lid is working in your favor. It is also important to consider what is being housed in the tank. If you have anything photosynthetic, you may want a schedule for wiping and cleaning off the lid frequently. As condensation builds up it can lead to a sediment build up hindering the light from penetrating the lid.
What should I do about water evaporation in my saltwater aquarium?
Water evaporation in a saltwater aquarium, much like a freshwater aquarium, will need to be replenished. All the same applies here for the pumps running dry and potentially burning out but there is one other element that must be touched on. When replacing evaporated water from a saltwater aquarium you should almost always use fresh reverse osmosis water (rather than pre-mixed saltwater). The simple reason for this is that water evaporates and salt does not. As the water level depletes in a saltwater aquarium the salt concentration remains the same. This will result in an increase in salt gravity.
If you do not make your own RODI water at home or at your place of work it is recommended to always buy an extra five or so gallons of RODI water from your local fish shop. This should be kept in a covered and safe container at the same temperature as the aquarium.
As a preventative measure, You should alway consider covering your aquarium with a lid. The Glass/plastic/acrylic lid or top may not totally stop water evaporation but it will help slow the rate. You may notice condensation on the lid - this will be a clear indication that the lid is working in your favor. It is also important to consider what is being housed in the tank. If you have anything photosynthetic, you may want a schedule for wiping and cleaning off the lid frequently. As condensation builds up it can lead to a sediment build up hindering the light from penetrating the lid.
What should I do about water evaporation in my sump?
If you are running a sump on your aquarium you will have a chamber or compartment in the sump where the water level will be falling and rising as water evaporates or as water is added. It is important to focus your attention on this single chamber when thinking about water evaporation. This will be across the board, no matter what design the sump is - it will always be your return chamber (or the last chamber before returning up to the display). As this chamber is smaller in volume that the other chambers and whole tank combined, it will be critical to watch this water level. As mentioned above this is where your return pump is housed and as water evaporates from the aquarium this chamber will lower and ultimately ruin the return pump if left to run dry. Just because this is the chamber that falls as water evaporates does not mean this is specifically where water needs to be added. Fish tanks are closed loop circuits, meaning the replacement water can be added anywhere. It is important to note to watch this compartment as water is added to accomplish the desired water level.
Sumps create more open surface area where water can evaporate. As a preventative measure, if the display tank (upper portion of the system) is covered with a lid this will help. In the spirit of the sump discussion, depending on what equipment is housed you may find it beneficial to add glass or acrylic top to some of or all of the sump area. This will in turn keep evaporation and condensation from leaving the tank or system thus slowing the evaporation rate slightly.
As a quick note, due to the smaller compartment it will seem as though water is rapidly (quicker or more than normal) evaporating when in fact the rate of evaporation remains the same. The compartment in which the level is falling is simply smaller and will need to be replenished more often to avoid pump failures. This will be a good segway into ATO systems.
Should I get an auto top off (ATO) system?
After talking briefly about sumps and how the water level will be forever fluctuating it would be recommended to incorporate an auto top off system. This system is similar to how the back of the toilet fills to a certain level and then stops after flushing. Here after water has evaporated a float valve or an optic eye sensor will trigger a pump in an external reservoir to refill the return chamber to a desired height. When the optic eye or mechanical float valve falls under the desired level, it will trigger a DC relay to activate the pump in the external reservoir. As the water is pumped over and the level rises in the chamber either the optic eye will sense the level and shut the pump off or the float valve will float into the off position, opening the circuit in the relay shutting the pump off. There are many commercially available ATO systems on the market that will be “plug and play”. In other words, understanding the internal electronics should be unnecessary and a basic implication will be all that is required.
Another way to auto replenish water would be to use gravity. Again, a float valve will be installed at a desired level and your external reservoir would be placed above the sump. When water evaporates, the float valve will drop letting in water to replenish evaporated water and when the level rises the float valve will rise and shut off the supply of water automatically. An ATO is one of the most common upgrades to a system that involves a sump. This will not only provide an ease of mind but will also promote stability in the aquarium.
