Water changes, a thing of the past or necessity of the present?

Water changes are one of the best maintenance practices that can be performed on any marine aquarium. They remove nutrient laden water and replace it with fresh, nutrient free water. When RODI purified water is employed, a good salt mix is able to strike a perfect balance of elements, simply by adjusting the mix’s specific gravity to normal reef levels. After a water change; calcium, magnesium and carbonate is replenished and trace nutrients that filtration was unable to remove are diluted. At one time, water changes were the primary way of both balancing water chemistry and quality.

Sadly, water changes are one of the most laborious ways to maintain a reef aquarium. Even worse, they are environmentally wasteful. Even efficient RODI units usually create four gallons of waste water, per one gallon of purified water. Most of this waste water runs down a drain into a septic tank or public sewer system. Creative aquarists have established rain barrels and grey water management systems. Some simply use RODI waste water to fill washing machines or other appliances that need fresh-water to function. Just using a RODI unit is expensive and time consuming. Most units make between 70 -100 gallons of water daily. Once you’ve got fresh water, it must be heated, stored and brought to the appropriate salinity. The water change itself takes time, as often large amounts of water must be pulled from the tank and then pumped in from a reservoir for replenishment. All this equals more waste, more time and yet another frustrating chore.

Reef tank technology has changed how we gauge when an aquarium needs a water change. Before, many aquarists planned a change at specific intervals (once weekly, twice monthly, etc). Some aquarists conducted a water change when nitrate reached a certain concentration, or when ph began to drop. Others changed water when calcium or carbonate levels began falling. These are still wise ways to decide when your tank’s water needs changed. However, dosing pumps, calcium reactors and efficient de-nitrification filters have greatly reduced the need for water changes. In fact, if you employ these devices, a water change could literally cause more harm than good, by overloading your tank with elements it simply doesn’t need. So are water changes necessary into today’s aquarium age? Can aquarists once and for all put away the buckets, Brute trashcans and household water pumps?

Aquarium tech’s effect on the water change:

Today, it’s economical and efficient to employ systems that ensure stability within a reef aquarium. Inexpensive devices like kalkwasser stirrers and ph controllers can maintain both calcium and carbonate concentration, while ensuring that ph remains stable at all times. More advanced devices, like controllers and calcium reactors can manage replenishment in even the most demanding reef aquariums. Automated dosing pumps can fill in the rest, replenishing everything for magnesium on down to specific amino-acids. Conductivity probes and automatic top off systems ensure salinity barely fluctuates. Add to this de-nitrification filters that absorb phosphate and convert nitrate into nitrogen and suddenly the need for water changes is reduced by well over 90%. Further reducing the need for water changes are automated mechanical filtration (such as the Theiling Roller Mat) and powerful protein skimmers that strip aquarium water of solid waste. Most of this technology was originally developed for use in large public aquariums, where the opportunity to change over 100,000 gallons of marine water didn’t exist.

Even tinged or cloudy water isn’t a major concern, as ozone, carbon and ultraviolet sterilization can clear-up nearly any water clarity issue. At face value, it would seem like for some aquarists, water changes would be entirely counterproductive. An issue that is common among some aquarists, is the use of water changes in conjunction with the equipment just described. Since the automated systems keep calcium, alkalinity and magnesium (along with other elements) in check, conducting a water change can over-replenish those elements, causing a sudden change in water chemistry. I once worked with an advanced aquarist, struggling with a calcium concentration of 600 ppm and a dKH over 14. He didn’t understand how, with all his advanced equipment, water chemistry was so out of whack. The problem ended up being his weekly water change. The aquarist was replenishing a balanced, mineral rich water content with mineral rich water, much faster than his livestock could utilize calcium, magnesium and carbonate. He needed less water changes and after switching to a once monthly (over a once weekly) water change schedule, his issues resolved themselves.

Today, there are even systems (such as the Triton method) designed to not only eliminate the need for water changes, but also carefully monitor water chemistry. I’ve personally visited thriving tanks that haven’t had a water change in years.

So, why change water:

Turning your aquarium system into a fully automated, self-maintaining machine is beneficial in many ways. It greatly reduces micro-management and intervention on behalf of the aquarist. However, it’s not without cost and concern. It also encourages a “hand’s off” approach to husbandry. Suddenly, aquarists become less critical of their tanks, assuming that the “systems” in place are doing their job. Sometimes, we can become overconfident in our devices, especially after months and months go by, with every element checking out and the tank seeming steadfast stable. We cease weekly testing, stop sending water into Triton and kick-back and simply enjoy our tank’s aesthetics. For many aquarists who employ automated reactors and controllers, the first thing to go are those pesky water changes.

Yet a water change isn’t just a way to replenish trace elements and reduce nutrient load. It’s a commitment to spending some time under your tank’s hood, inspecting things close and fixing all the little frustrations that pop up within any tank. Usually, all the aquariums equipment is turned off, meaning that current ceases and the aquarist gets a good view of all the tank’s nooks and crannies. Water changes are often the perfect time to treat aiptasia anemones, siphon out flat-worms, asternia starfish or other pests and clean up patches of un-wanted algae growth. They are also the perfect time to secure corals prone to falling over, fix wobbly rocks and give your tank an overall evaluation.

Also, they are perfect for up keeping all the equipment we rely on. Pumps are notorious for filled up with sludge, skimmer interiors famous for getting algae ridden and tubing infamously fills with debris. All of these issue sooner or later reach a head, resulting in a leak or equipment failure. Having a routine schedule that allows you to shut everything down and maintain the entire tank all at once, keeps the aquarist abreast of any potentially disastrous problems. Like any multi-faceted machine, our aquarium’s many devices breakdown over time and need routine maintenance, maintenance that is often hard to provide when the tank is full of water and all the equipment is running. Routine maintenance often stirs up sludge and debris, so pairing it with a water change allows aquarists to siphon debris out, before replacing water.

A kind of insurance policy:

When we rely on our bio-filter and specialized equipment to remove waste, often the entire tank is consistently running at full load. This means, the bio-filter and all applicable reactors are at saturation, they are keeping nutrient levels down, but they are at capacity. If any bacteria die off, or a circulation pump stirs the sand-bed, the resulting nutrient increase will max-out filtration systems, thus greatly raising nutrient load quickly. When this happens, a tank can spiral out of control and often water chemistry shifts, causing all sorts of unforeseen issues.

Maintaining an appropriate water change schedule can ensure that your tank’s water isn’t consistently at capacity. Nutrient load and water chemistry have a bit more wiggle room, since excess waste is removed during the water change and trace elements are entirely replenished. Completing a water change weekly or bi-weekly, gives aquarists the assurance that they’ve recently maintained their tank, along with all its associated peripherals, reducing the fear that something catastrophic is just around the bend.

Water changes that help, don’t hurt:

At face value, it seems like modern aquarium technology and methodology has eradicated the need for water changes. There are even systems that recommend abandoning water changes altogether. However, it’s likely that no amount of technology will ever totally remove the need for water changes, along with other responsible aquarium management protocols. What aquarium technology has successfully done, has reduced the need for very frequent, large water changes. While it was once common to remove 25-35% of a tank’s total water volume weekly, today a well-equipped tank can easily get by with a 10% weekly water change, or a 15-25% bi-weekly water change. The value of a water change isn’t just in the amount of water that is switched out, but also in taking the appropriate amount of time to conduct a thorough overview of the aquarium.

It’s vital to allow yourself ample time to both brew new saltwater and conduct a water change. Neither are something that should be rushed, or simply thrown together on the fly. I prefer to conduct water changes at a time that I know few distractions will arise, and I allow myself extra time in case I encounter something I didn’t expect.

Looking at large public aquariums can really help home aquarists understand the importance of water changes. When I worked at Pittsburgh’s PBG Aquarium, it was impossible for us to import or make the amount of water needed for a water change of the aquarium’s marine systems. One tank alone was in excess of 100,000 gallons and the city is located inland, so there is no marine water in site. This meant that the only way to improve water quality on a mass scale, was to pump marine water through a network of extensive filters. This was time consuming and expensive and not nearly as effective as a complete water change. These issues can leave inland public aquariums at a disadvantage over home aquariums or seaside facilities, simply because they don’t have access to fresh marine water.

Even at seaside aquariums, large volumes of natural seawater are often pumped in and undergo rigorous treatment with ozone or UV sterilization, so that a complete water change can be conducted. Considering that public aquariums often employ the very best in state of the art water filtration, this makes a powerful statement in favor of partial water changes.
About author
Jeremy Gosnell has been a marine aquarist for nearly all his life. While studying sociology in college, Jeremy pursued becoming a professional scuba-diver, eventually serving as a coral reef biology science instructor for the Beautiful Oceans Academy based in Montreal, QB. This took him around the world, exploring some of the planet's incredibly diverse coral reefs.

Also, Jeremy worked on staff at the Pittsburgh Zoo's PBG Aquarium. He has contributed to a variety of aquarium-related publications over a 15 year career including, Freshwater and Marine Aquarium Magazine (FAMA), Aquarium Fish International (AFI), Fish Channel, Tropical Fish Hobbyist Magazine (TFH) and reefs.com. Today, he serves on the content review, editorial board of TFH Magazine in addition to providing original content for online and print publications.

He is also the author of novella Neptune's Garden and novel The Terminal, which won a merit of science fiction award at the 2015 Guadalajara International Book Fair.

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