The most time consuming and least pleasurable task that needs to be done is a water change. There has been much debate as to whether water changes are necessary or not, as well as how often and how much should be changed. After much discussion, the general consensus is that doing regular water changes is crucial to the long-term success of every reef tank. It allows for detritus (and other large pieces of material) and undesirable compounds to be removed from the tank. It is important to do regular water changes because, despite advances in filtration methods, harmful compounds still tend to accumulate in a tank over time. Removing them in bulk during a water change puts less pressure on the live rock and filtration system to break them down. As a result, nitrate and phosphate should not accumulate as quickly.
Most experts now recommend approximately 10% water change per month. This small amount helps to remove bad compounds as noted, and helps to replenish trace elements as well. These small water changes will not dramatically reduce anything as their small size will only reduce things by 10% if that is all the water that is being changed. If some water parameter is really out of whack, then a larger percentage change will be necessary in order to dilute it out.
To do a water change, a clean garbage can or other vessel should be used to store the water during the change. Clean new water is mixed with salt to match the salinity of the tank and allowed to sit in the holding container for at least a couple of days with an airstone or powerhead in it. The water should be “cured†for a few days as freshly prepared saltwater is very caustic and if it is added to a tank before these caustic properties are reduced it can damage corals and even live rock. The proper amount of salt needed should be weighed or measured out so that at future water changes the needed amount can be simply scooped out. A powerhead rests on the bottom to aid in mixing and to keep the water moving and well aerated. The temperature of this water is heated to match the temperature of the tank.
When it is time to make the change, tank water is drained into buckets to match the desired amount of water that has been prepared. Once the proper volume has been removed, you may wish to mark the tank with a marker at this level. This will allow you to eliminate the troublesome use of buckets during future water changes because you can use the mark to determine the right amount of water to empty directly into a sink or drain. This mark should be on the sump if one if used, or on the tank itself. Taking this step to make future water changes as simple as possible makes it more likely that it will be done regularly.
To expedite the water change and to minimize the time that some of the live rock may be exposed to air, a powerhead can be attached to the refill line from the clean water tank or bucket. This step makes it possible to do a 10% water change on just about any size of tank in as little as 10 minutes.
During a water change, as much detritus, dirt, and algae as possible should be removed from the tank. A bulb baster should be used to squirt the live rock to help dislodge any detritus that has settled there. This helps to keep any long-term dead spots from forming and reduces the likelihood of an algal bloom.
The nature of the tank should be noted when doing water changes. That is, a water change is only beneficial when the new water is of higher quality than the water it is replacing. Since water from many water companies is less th an optimum quality many hobbyists have found it advantageous to invest in either a deionizer or reverse osmosis unit for water purification. These units act to remove harmful chemicals and metals from tap water. In most instances they are necessary for a marine aquarium.
Doing a water change on a regular basis is a necessary task for virtually every aquarium, but especially for a reef tank. The inhabitants we keep are accustomed to pristine water free of the build-up of toxic compounds. Only by doing water changes on a regular basis with good quality seasoned water are we able to replicate and maintain the conditions they require.
