Weekly Water Change & Aquarium Maintenance Routine | Saltwater Aquarium Beginner's Guide: Episode 8
Water changes get a bad reputation in the aquarium hobby. They're often talked about like a dreaded chore that should be avoided at all costs. In reality, they're neither complicated nor time consuming.
A reef tank isn't living wall art. It's not a picture frame you hang on the wall and admire from across the room. It is a collection of living animals that depend on you for clean water and consistent care. Just like walking a dog or cleaning a litter box, aquariums come with ongoing responsibilities, and water changes should be part of that routine.
Once you accept water changes as standard tank care, they stop feeling like a big event and start feeling like just another habit. With a simple, repeatable process, they become easy to manage and play a key role in keeping a reef tank healthy long term.
What Does a Water Change Do?
A water change is simply the action of removing water from the aquarium and replacing it with clean water.
Aquarists use water changes to:
- Clean the sandbed
- Scrape algae from the glass
- Remove and dilute excess nutrients from the water
Can I Run a Saltwater Tank Without Water Changes?
We don't recommend maintaining an aquarium with zero water changes.
Mature systems may require fewer or smaller water changes, but these tanks often have comprehensive filtration systems and are packed with mature coral colonies that uptake nutrients quickly. These systems are run by experienced reef keepers who understand the risks and tradeoffs of not performing water changes and often do frequent water testing.
How Often Should I Do a Water Change?
Weekly, every other week, or monthly are the most common water change schedules for successful saltwater aquariums.
- Weekly: Best for new reef keepers or new aquariums that are less stable
- Bi-Weekly: Good for aquariums that are more established and have good filtration
- Monthly: Good for mature aquariums with solid filtration in place
How Much Water Should I Change?
Matthew changes 30-50% of his aquarium's water weekly, but depending on your aquarium size, that may or may not be practical.
For example, if you have a large 200 gallon aquarium, changing 100 gallons per week is going to be tough. As a general recommendation, try to do at least a 10% water change.
Let's Go! Here's the Step by Step Method Matthew Uses
We're going to assume you've mixed your fresh saltwater ahead of time. If you haven't, stop and do that now before proceeding.
Learn How: The Best Methods For Mixing Saltwater
Step 1: Routine Water Testing
Take a water sample and perform your weekly water parameter tests. These results may influence how big of a water change you perform.
Matthew tests weekly for:
Salinity
Salinity generally remains stable and won't need to be touched, especially if you're running an auto top off system.
Alkalinity
If too low or high, make adjustments to your dosing routine.
Nitrate
Matthew considers 20 ppm or above high and will do a 50% water change if they're at this level or trending up.
Phosphate
Matthew considers 0.15 ppm or above high and will do a 50% water change if they're at this level or trending up.
Step 2: Heavy Feeding
This might sound counterintuitive, but this is the best time to do a heavy feeding. Any uneaten fish or coral food can be easily removed when we do our water change.
Matthew feeds his tank:
- Frozen Mysis Shrimp
- Reef Chili Coral Food
- Seaweed Extreme Pellets
- BRS Fish Food Pellets
- Nori Sheets or Algae Wafers
Step 3: Clean the Glass
As the fish and coral are eating, take the time to clean the glass. We like to use a magnetic algae scraper, but a handheld scraper will do the job too.
Magnetic Glass Cleaner Tips:
- Go slow near the silicone seams to avoid damaging your aquarium.
- Go slow near the sandbed. If sand gets trapped between the magnets, it can scratch the glass.
- If you don't store your glass cleaner in the tank, rinse with freshwater before storing it.
Step 4: Siphon the Sandbed
We made it! The actual water change starts here. Turn off everything but the lights.
Before we get started, it's important to mention these tips:
- Only clean about a quarter of the sandbed at a time. This helps reduce the impact on the biological filtration system.
- If you have a deep sandbed, only clean the top 1" so that you don't disturb the anaerobic bacteria toward the bottom of the sandbed.
How to Clean the Sandbed:
- Start a siphon with your gravel vacuum
Not sure how? Learn Here: 5 Ways to Start a Siphon for an Aquarium Water Change - Place the gravel vac tube in the sandbed and wait until the sand reaches about 3/4 of the way up the tube.
- With your free hand, firmly pinch the flexible tubing to stop the water flow.
- Lift the gravel vac and let the sand fall back down to the bottom
- Move the gravel vac to a new spot and stop pinching the tube
- Repeat this process until about 25% of the sandbed is cleaned
Step 5: Continue Removing Water & Add Any Maintenance Supplements You Rely On
Continue removing water until you reach your targeted water change volume. Once you're done with that, it's a good time to add any maintenance supplements you rely on.
In Matthew's case, he regularly adds Brightwell CoralAmino and MicroBacter7.
CoralAmino
A concentrated amino acid supplement designed to support coral health, coloration, and growth. Amino acids are a key building block for coral tissue and can help corals recover from stress and make better use of available nutrients, especially after routine maintenance like water changes.
MicroBacter7
A blend of beneficial bacteria that helps maintain biological balance in the aquarium. It supports nutrient processing, reduces excess organics, and promotes a stable microbial environment, making it a common addition after water changes to reinforce the tank’s biological filtration.
Step 6: Swap Filter Socks and Start Refilling with Saltwater
Take this opportunity to swap out your filter socks or any other mechanical filtration.
Make sure your freshly mixed saltwater matches the aquarium's temperature and salinity level, then start slowly refilling the tank.
Tips:
- Use a pump and tubing to refill the tank. No lifting buckets or jugs required!
- Don't walk away from the tank while you're refilling. Bad things happen...we don't want to talk about it.
- For all-in-one aquariums, refill into the rear filtration chamber to disturb the main display the least.
- Keep any UV sterilizers off for a couple hours if you've added any bacterial supplements like Matthew did
Step 7: Refresh Carbon and GFO Based on Your Nutrient Goals
Carbon is exhausted quickly in a reef tank, so using less, but changing it more often is ideal. Changing carbon weekly will give you great results.
For GFO, if and how much you add will be dependent on your phosphate levels, so review your test results from step 1 and go from there.
Activated Carbon
Used to remove dissolved organics, toxins, and compounds that cause yellowing in aquarium water.
Granular Ferric Oxide (GFO)
A phosphate-removal media that binds excess phosphate as water passes through it.
Step 8: Quick Final Checks and Cleanup
We're almost there! As a last step, we'll check and refill the ATO reservoir if needed and wipe down any salt creep, splashes, or spills with a clean rag.
Clean the outside of the glass with RO/DI water or an aquarium-safe cleaner and microfiber towel and your tank will be ready for next month's Reef Tank of the Month competition.
Last but not least, discard the dirty saltwater if you haven't done so already, then sit back and observe the tank for a few minutes to make sure the fish, corals, and invertebrates are acting as expected.
Having a Hard Time Sticking to Your Aquarium Maintenance Routine?
We've been maintaining aquariums for decades around here and we totally get it; aquarium maintenance is easy to let slide. Skipping one water change leads to skipping two. Then you look up to realize you haven't done a water change in months and algae is starting to cover the rocks.
Here are some tips we've found helpful to keep you on track:
Put it on the Calendar
When it comes to the bigger stuff like a water change, having a set day of the week to do it keeps you in the groove.
Tie Maintenance to Another Habit
Pair tank maintenance with something you already do regularly, like while listening to the pre-game for the weekend game. Stacking habits makes them easier to maintain long term.
Keep Supplies Organized and Accessible
This might seem obvious, but when your aquarium maintenance gear is all over the place, water changes feel like the world's worst scavenger hunt.
Set up a Water Mixing Station
A dedicated area for salt mixing is such a game changer. It doesn't have to be fancy. Even a corner where you can mix salt in a couple 5 gallon buckets makes it easier.
Start Small
You don't have to do all of your weekly aquarium maintenance at once. If you notice a patch of algae starting to grow, take 5 minutes to reach in and remove it before it becomes a larger problem.
Remember Why You Are Doing It
A water change is like going to the gym. You won't notice much difference after going once, but the results add up over time.
Adam has been reef keeping since 2010 and got his start on the Bulk Reef Supply Customer Service team. He believes the best tanks are built around what you enjoy, not what’s trending. Adam is especially interested in simplifying the hobby, exploring the latest gear, and helping others focus on long-term success over chasing perfection.
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