The general consensus about water changes in a reef aquarium among aquarists is that YES, they should be done, and regularly. The percentage and how often vary from person to person, but a general rule is at least every couple of weeks, and at least 10% -20%. The main reason to do water changes is to decrease the ammonia and nitrate levels in your aquarium. These levels can be harmful to the life in your tank, and exchanging a percentage of the bad water with fresh water helps with this. Another reason to perform water changes, even if these levels are zero, is to replenish the 70 or so trace elements that may be depleted in your tank, which is why using a high quality salt mix is important. You may not be aware of what levels of these trace elements are low because you don’t test for most of them, so changing the water regularly is a safe way to ensure you are maintaining saltwater as close to natural levels as possible. The salt mix we use is AquaVitro Salinity by Seachem.
Because our tank is so new and has a very low bio-load, we technically may not have to perform water changes as often as others right now, but we have been doing one every 2-3 weeks regardless. Using cured live rock helped decrease the amount of water changes needed in the initial cycling period, and since our tank is so new (2 months), we have only performed 4 of these water changes so far. This is how we do our water changes:
We have set up an RO/DI unit in our basement that supplies us with the perfect water needed for a saltwater aquarium. RO/DI stands for Reverse Osmosis Deionized Water.
Our well water flows into the filtration unit, and the result is RO/DI water that then goes into the top bin on our shelving unit.
We use the RO/DI water daily for topping off the tank, which is just replenishing the water that has evaporated. It is approximately one gallon for us, and we use a milk container for this to transport it from the basement, upstairs to the display tank.
It is important that any and all containers used in aquariums are considered food grade, meaning you can eat from them. This consists of plastics with these symbols:
It is also very important not to wash these items with soap. Soap is bad for your tank so make sure that anything you use for your aquarium is completely free of soap and soap residue, even your hands.
When we need to do a water change, we syphon the RO/DI water from the top bin, to the bottom bin. We then measure the salt using the recommended amount from the back of the salt container and use a circulating pump for 24 hours to mix the salt.
We only make saltwater as we need it, but saltwater can be made in advance and used as needed. Because our saltwater is stored in the basement where it is cooler, and we do not warm it until we are ready to use it, we are not concerned about it growing any bacteria or becoming rancid, as long as we keep it circulating.
When we are ready to perform the water change we will use a heater to match the temperature in the display tank. We then match the salinity using a refractometer. Adjustments to salinity can be made by adding a little more salt or more RO/DI if needed.
Prior to exchanging water, we use a turkey baster to clean off the rocks of any fish poop and other debris before we start the water change. This works surprisingly well. I was also surprised at the amount of fish poop and other detritus on the rocks that you can’t really see. I would highly recommend this step.
We also use a gravel vacuum to help suck up this debris, as well as to filter some of the substrate.
Some aquarists will suggest not using a gravel vacuum, or using one sparingly so as not to disturb too much of the anaerobic bacteria that are essential in the breakdown of nitrates, completing the nitrogen cycle. It is also cautioned that too much vacuuming will release a lot of nitrite and nitrate into the aquarium, producing a spike in these levels that could be detrimental to the life in your tank. We choose to vacuum lightly, and only small parts of the substrate at a time, and only during water changes.
The above gravel vacuum syphons the sand by allowing the detritus to be syphoned out, and the heavier sand to fall back onto the sandbed. This gravel vacuum has a regulator allowing the water flow to be increased or decreased. We syphon approximately 10 gallons of water out into 5 gallon buckets, and then take these buckets back down to the basement. The waste saltwater then goes into our sump, out to a dry well, and into the ground.
We then haul the fresh saltwater up from the basement, using the same 5 gallon buckets, and poor it slowly into the tank, trying not to disturb too much of the fish, corals, or sandbed.
Performing water changes seems daunting, but once you get a method down its pretty easy, especially with two people. It does take some planning in advance however, so make sure you monitor your water chemistry levels regularly so you know when you need a water change. Don’t wait until the chemistry levels are high or toxic before deciding to do a water change.