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Photo by: Juliana Buglia

Water changes are one of the key maintenance items you should do to keep your saltwater aquarium and it’s inhabitants healthy. Different hobbyist’s each seem to have their own preference for how frequently water changes should be performed and what percentage of water should be changed. This article details my preference and my particular process. Understand, you will need to determine your own comfort level for frequency and how much water should be changed based on the needs of your aquarium and it’s inhabitants.

One of the important things I’ve learned in the 20+ years I’ve been doing aquariums is that each aquarium is unique and requires difference maintenance. More importantly I’ve learned that each aquarium’s maintenance needs will change over time as well. For example, my current 75-gallon saltwater tank required far more maintenance during the first few months that it does now. Regardless, water changes have been the one thing I’ve kept consistent. While during the first few months (after cycling), I did water changes weekly, now that my tank has stabilized I only do them every other week.

Why do water changes?

Water changes are important for many reasons, but here are the top reasons:

• Replenish necessary minerals needed by the aquarium and it’s inhabitants. Primarily calcium, magnesium.
• Remove pollutants from the water. Over time, due the inhabitants of your aquarium, it will have a slow buildup of pollutants that aren’t healthy when present in high levels. These include things like Ammonia, nitrates, Nitrites and Phosphates. Water changes dilute and remove these pollutants making for a less harmful environment for your inhabitants to live in.
• Remove detritus from the tank A water change consists of removing water from the tank and adding new water to the tank. Removing is generally done using some type of suction device, typically a hose. Water changes provide an excellent opportunity to suction off the detritus (aka fish poop) from the sand and rock before it can break down into more harmful chemicals such as ammonia.

How often should water changes be done?

If you ask 10 saltwater hobbyists, you’ll get 10 different answers to this question. Most will agree however that at the very least 10-20% of the water needs to be changed monthly. I would recommend starting off by doing weekly 10% water changes and then based on how the tank is doing, amount of detritus, levels of pollutants, and clarify of the water adjust.

I started doing 10% water changes each week, and continued to do so for a good 8 weeks until my water parameters reached the correct levels. I then switched to doing bi-weekly 20% water changes, and have continued doing those for the past few months on my current 70 gallon tank. While your fish and corals may seem to be fine with infrequent or no water changes, they will do far better with water changes.

If your saltwater tank is still cycling, you should not do water changes until the cycle is complete. You should only be adding unsalted top off water.

Mixing the water

This sections begins describing the process I use for mixing saltwater and doing water changes. I adopted my process based on lots of reading in the 3Reef forums and from two videos I ran across on YouTube by LimpitsReef who has an excellent video on how he does his water changes. The video is divided into two parts, Part I and Part II. I encourage you to use whatever process works for you, but hopefully between LimpitsReef’s videos and my description, you’ll get a good baseline and some ideas.

Mixing the water is a step that most new hobbyist’s don’t pay much attention to. They go grab a bucket of tap water, add a dechlorinating product to it, throw in some salt, mix it up and poor it in the tank. I promise you, this process won’t work well for long.

First, it takes time for the salt to completely dissolve and fully mix into the water. I’ve found this to be at least 6 hours. The temperature of the water is also critical, as the salinity of the water changes based on the temperature of the water. The type of water you use is critical as well. I use only RO/DI water. I started using tap water initially, and had huge algae and fish health issues. Switching to RO/DI water is one of the best investments I’ve made.

I store my water in a 30-gallon food safe trashcan. I use a Rubbermade Brute Trashcans for both my saltwater mixing container and for my RO/DI waste water tank. I first filled one of the trashcans with four buckets of water and added additional water until my water level was four inches above the level reached with the four buckets. I then marked the water level using a permanent marker. This would be my fill level (I’ll explain the additional 4 inches later). I then emptied the trashcan (using the water on our flowers) and marked the top of it “Saltwater Only!”. I then marked the other trashcan top “Waste Water Only”.

I then drilled small holes in the top of each trashcan, and put the RO/DI filtered water tube down in one, and the waste water tube in the other. I keep my water cans in my garage where my RO/DI filter is.

I then turned on my RO/DI filter and started timing how long it took to fill the saltwater only bin with RO/DI filtered water. Anyone who is familiar with RO/DI filters knows that they generate, on average, 3-5 gallons of waste water for each filtered gallon of water. Some quick math will show you that my waste water container would fill up before my saltwater only container. Oops! In the short term, I just timed how long it took to fill up the waste water container. Emptied it, and then timed again how long it took to fill the saltwater only tank to my water mark.

When the waste water container fills up the first time, I just empty it out. Typically, I use the waste water on my wife’s flowers and trees, and then restart the RO/DI filter. A better solution would be to have two waste water containers, and connect them at the bottom with a piece of PVC piping, effectively doubling the size of the waste water container. I’ll be doing this soon. Another solution is to buy a waste water container big enough to hold the waste water. This would be an even better solution!

Once the saltwater only container is filled to the water mark with good quality RO/DI water, I then add the salt. I use Instant Ocean salt mix, but many other brands work just as well. The first time I did this, I counted the number of cups required to get the salinity to 1.025 (the level I keep my tank) wrote that number on the top of the saltwater only container. This way, each time I mix water, I know how much to add.

Hey Saul, didn’t you say salinity is dependent on the water temperature? Ah, yes I did. I have a 200watt submersible heater that I keep in bottom of my saltwater only container, along with a floating thermometer. I have the heater set to 80 degrees, the temperature I keep my tank.

I also purchased a large water pump to go at the bottom of the tank. The pump has dual use: 1) It keeps water flowing in the saltwater only container to avoid stagnant water, keeps the water well aerated and mixed 2) I use the pump to pump the water out of the saltwater container and into buckets when I do my water changes. This is the reason for the extra 4 inches of water I mentioned earlier. Without the extra few inches of water, the pump will start to suck air and you won’t be able to easily get all of the water out of the container.

I generally let my water stand mixing for 3-5 days prior to doing the water change. This is sufficient time for the salt to completely mix, temperature to adjust and for me to check the PH level and adjust it if necessary. Although I seldom have to adjust the PH, I always check it. The Instant Ocean salt mix seems to get the PH correct right out of the bucket.

Removing water from your tank

Now that we’ve mixed the water, have it at the right temperature, and adjusted the PH, it’s now time to actually pull some water out of the tank. One of the most important things I should mention is that that you ensure you have a good hour of uninterrupted time to dedicate to doing the water change. I say this because for my water changes, the water level drops below the skimmer intake, and below my two circulation pumps. As a result I turn these off while I’m doing the water changes. The longer your pumps are off, the more risk to your tank due to lack of flow and due to dropping PH.

For my water changes I use 2 5-gallon buckets. My buckets are clearly marked Saltwater Only. They are never used to to hold anything else in order to avoid accidental contamination. I use a siphon based gravel cleaner to siphon 4 buckets of water out of the tank. While siphoning the water, I stir up my sand a little, and run the gravel cleaner just over my live rock to remove any detritus that might be laying around. This water is flushed down the toilet.

Refilling the tank with fresh saltwater

I rinse out the buckets to remove any residual detritus or sand that might be hanging around and then head to my garage to start the refill process. To pull water from my saltwater container, I use the same pump that is normally used for circulating and mixing my saltwater. I first turn the pump off, then connect a piece of clear tubing approximately 6 foot long to the pumps output. I then put the other end of the tubing into one of the buckets and turn the pump on. This allows me to quickly fill both buckets.

I then carry the buckets into the house and poor the fresh saltwater into my tank SLOWLY to avoid disrupting the sand bed, live rock, and corals. I then head back out to the garage, fill both buckets again and finish filling the tank.

Wrapping Up

At this point, we’re about done. I usually keep a towel with me at all times to clean up any minor (or major) spills and also use this towel to dry off the top of the tank to reduce salt creep. I then rinse out all of my equipment, and hang it back up in the garage, placing my buckets upside down to avoid dust and dirt from getting in them.

That’s about all there is to it. As I said before, this is just my way of doing my water changes. I remove my water and add water straight into the tank, as I don’t yet have a sump. If you do have a sump, water should be removed from the main tank, and new water added to the sump as LimpitsReef shows in his video.

One last tip: If you are able to mix your saltwater on the same floor where your tank is, I’d highly recommend investing in the Rubbermaid dolly designed to fit on the bottom of the Rubbermaid Brute Trashcans. This will remove the need for buckets as you can siphon water out of your tank into a trashcan, and then pull your saltwater container into where your aquarium is and re-fill your tank straight from the container. I don’t have this luxury, but if you do, it’s a great option that will save your back and keep you from spilling water on the floor as the water slushes around in the buckets.