We are asked this all the time: “Is it absolutely necessary to perform regular water changes?” Let us waste no time in answering that question: Yes! Yes, water changes are certainly necessary. While some tanks need them more often than others, there’s no denying that regular water exchange improves water quality. And it accomplishes this much more easily and at a lower expense than dealing with an enormous amount of additives and chemical filtration media.
There are lots of reasons to change water in a reef tank. Or a freshwater aquarium, or pond, or whatever. It all boils down to two objectives: Removing excess substances and replenishing depleted substances. Seawater (natural or otherwise) is basically an insanely complex soup of organic and inorganic chemicals. Some of these are essential, whilst some are poisonous. Many are actually required for healthy ecological functioning, but are nevertheless toxic at unnaturally high concentrations (ammonia, iodine, etc.).
Water changes change everything
Sure, fine, it’s true. You can test for many of these “parameters.” Current ICP testing technology is downright amazing. You can now “chase” any exotic parameter if you so wish. But would you really want to? Think about it for just a second. You already do (and should) analyze your system water for the “basics” such as nitrate, phosphate, calcium, pH and so on. These are hardly the only factors that can make or break your aquarium. Consider loss of many essential trace elements, which few hobbyists can easily test for. Consider also the accumulation of toxic metabolites (allelopathic substances, for example), which few hobbyists can easily test for. The sad irony is that micromanaging your aquarium system–just to avoid water changes–can still leave that one fatal chemical that jacks up everything.
It’s really, truly, weird how long the goal of avoiding water exchange has stuck around in the hobby. In some cases, the supposed virtues of shirking water changes were touted by manufacturers with the claim that a product they peddled would eliminate the need altogether. Some hobbyists like to boast of how well-built or well-maintained their system is on the basis that they hadn’t changed any water in x number of months. Curiously, even proponents of natural aquaria like to use this as a metric of how balanced their system supposedly is.
Well, let’s be absolutely clear here: There’s nothing unnatural whatsoever about water exchange. To the contrary, this is exactly what happens on a natural coral reef environment, every single day, as tide waters bring in “fresh” new water and flush out the old. Think of water changes in your tank as replicating these very same, very natural, processes.
At the very least, think of all the time and money you’ll save. In the noble quest to avoid having to fill and empty a few buckets of water every weekend, some aquarists end up taking on a second job as biochemical engineers. And burn a hell of a lot of cash in the process. Added up, all the additives and filtrates some hobbyists use can amount to a small fortune in little time. They certainly cost more than few buckets of saltwater.
Don’t get us wrong here… We do see the advantage of using a high-quality GAC or DI resin, for example, to enhance/stabilize your captive ecosystem. What we’re saying is that mitigations such as these should only be used, if needed, after an aggressive water exchange regimen has already been put in place. We stand by the old-school general guideline recommending a monthly 25% water change. We further agree that smaller, more frequent water changes (15-20% every 1-2 weeks) are even better. Weekly changes are ideal, as no parameter can get out of whack for very long before it is corrected.
We’re sure you’ve heard it before, but we’ll stress again here: Use only purified water for mixing saltwater (as well as for use as top-off). Tap water invariably contains impurities such as heavy metals and phosphates; thus, replacing your dirty tank water with salted tap water is counterproductive if not utterly bone-headed.
Similarly, using a subpar salt mix makes little sense. Thankfully, most of the mixes offered in the market today appear to be pretty well balanced and devoid of contaminants. Nevertheless, it’s certainly worth the peace of mind to place your trust in a mix that already has a great track record in the industry (e.g. Fritz RPM Salt).
Look, we’re not out to become the face of the hobby’s water change police. But come on… The benefits of regular water exchange are just too obvious. Reef aquaria are complicated enough. Why rely on an inordinate amount of water testing, equipment, supplements and so on when you can do it all, easily and without headaches, with a simple water change? The beauty is that you cannot overdose water changes (especially if they are performed at a high frequency in smaller volumes). And they fix so much at once; each one brings every imaginable parameter closer to optimal conditions. You can therefore think of them as a fail-proof one-button total reset. Few things in reefkeeping are that uncomplicated!