If there is a dead horse that’s been beaten, picked at by vultures and left to decompose in the hot savanna sun, it’s the topic of water changes. Now that the maggots, coyotes and other scavengers have had their way with it, I’ve decided to take another swing, cracking hard into the exposed skeleton of this long debated topic. Water changes represent the very basic level of marine or reef aquarium care, and in reality are the most archaic and simple way of removing unwanted nutrients, and balancing crucial water chemistry parameters. Take dirty water out, and replace it with pure water, what could be easier. Today, there are numerous gadgets that filter our aquarium water, and the rise of bio-pellets and zeolite even gives nitrate a run for its money. So is there really any reason for aquarists to be hauling buckets, making water and dealing with salt mix on a regular basis? Water changes historically:
I came to the marine aquarium hobby after keeping freshwater fish for many years. For a long time I bred the popular Discus fish, a South American cichlid that is known to thrive in very pristine, low ph water. It wasn’t uncommon, when trying to get Discus to make babies, for aquarists to do an 80% or even 100% water change daily. Needless to say, when I arrived at marine aquaria’s doorstep, I was well versed in regular partial water changes. Back then, regular water changes were part of general aquarium maintenance. Some reef aquarists were doing them three times per week, even completing small 5% water changes daily. It was before RODI units became popular, and typically we used warm tap water treated with a de-chlorinator. Back in those days, I did two 35% water changes per week, turning over 70% of my tank water weekly. When I stepped into reef keeping, I adopted the daily 5% water change schedule. Oddly enough, my tank was full of hair algae, brown algae and diatoms. Reality was, it didn’t matter if I changed 100% of my tank water daily, my source water at the time had traces of phosphate and nitrate, and I had no RODI unit to remove it. Since the weapon of choice those days was wet-dry filtration, high levels of nitrate were common, and often we didn’t worry about it unless nitrates exceeded 50 ppm. 
On the reef side of things, there was no “reef specific salt” so changing water was a tireless exercise in testing, additives, more testing, and a bit of luck.… More:
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