A drop of water.

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Automated Water Changes

Automation is all the rage these days, with a sizable percentage of reefers believing that a controller is essential to the keeping of a reef tank. It's not, but it is a nice-to-have as long as you are sensible about what you expect it to do for you ….. and not do for you.

For those of us in the hobby long enough to remember when there was essentially NO automation, the things that modern technology can do are pretty cool. One of those things is the ability to automate water changes. There are few more 'drudgerous' tasks than doing water changes. So much so that a cottage industry sprang up to try to make them unnecessary.

The Triton system, for example, maintains that water changes are unnecessary, and that tanks can thrive with proper nutrient export and complete dosing. I've not ever tried such an approach myself, but there are spectacular tanks run on the principles of no water changes. Most of us, though, do water changes as both an exporter of 'bad stuff' and a replenisher of 'good stuff', even if the precision is somewhat less clear. So, if that is broadly the why, let's explore the how.

Manual Water Changes

The easiest conceptually, but also the most tedious is the manual water change. If the readers are like me, it gets skipped far too often and can lead to general tank decline (the mythical old tank syndrome). You need a few buckets, some siphon hoses, the patience to mix up a batch of salt water and a youthful back to lug said buckets (or convince your wife that you require a teenaged son). Turn off pumps, siphon water out of tank, add water back into tank and restart pumps. Gads, how tedious …. and completely un-fun!

Semi-Automated Water Changes

This is the approach I took for a very long time. There are countless ways in which a semi-automated water change can be implemented. My own was to add dual 40B tanks to my system which could be switched in and out of the system as needed.


Photo is courtesy of Simon Ellis, ©2019, All Rights Reserved.

While the main siphon drain was running through tank A, I would mix up a new batch of salt water in tank B. Once ready, throw a few ball valves and the drain was rerouted to tank B. Voila, a 36-gallon water change (I still haven’t quite recovered from the shock of discovering that a 40B doesn’t hold 40 gallons; who knew!). The old water in Tank A could then be used for a quarantine tank or just discarded. Once empty, Tank A was refilled with newly made salt water.

Automated Water Changes

Although not without some manual effort, the best approach in my view is to do fully automated water changes. The manual effort is mostly in the making and disposing of the new and old salt water used in the automatic water change system. There are a couple of commercial models available, the Genesis Renew is one such system that seems to get good reviews. I have not used it myself so cannot comment on it either way.

My approach, as many other have done, is to use a dual head dosing pump – in my case, the peristaltic Apex DoS. You can use a wide variety of pumps, from continuous duty units like a MasterFlex to somewhat less durable, but also less expensive BRS units. I went with the DoS because I have an Apex, and they make the programming dead easy.


Photo is courtesy of Simon Ellis, ©2019, All Rights Reserved.

I dispensed with the dual 40B tanks in favor of dual 50-gallon brute cans. I went with that size to make mixing easier. I now just pour one of the 50-gallon bags of Instant Ocean into the bucket and add the appropriate amount of RODI water – no more scooping, and occasionally inhaling, salt mix.

At normal salinity, the 50-gallon bags don’t actually make 50 gallons (can nobody add anymore?) so the marked line inside the brute can is at about 45 gallons. I have an aversion to flooding my floors, so I installed a couple of float switches into each bucket to tell me when the new salt water (NSW) tub was empty or the old salt water (OSW) tub full.

I also have a backup optical high-level sensor in the OSW tub, just in case. The NSW tub has to be manually filled from my ATO reservoir, but the OSW drains directly into my slop sink with just the turn of a valve handle. It is not necessary to have the OSW tub. One could output old water directly to the house drain instead, but I like to be able to eyeball that the amount of water removed is broadly equivalent to the amount added. Since I use the Apex salinity probe, I could use that to ensure that the salt level is neither climbing nor falling.

As noted, setting up the DOS is really very simple. Once calibrated, it exchanges the full 45 gallons over a period of 10 days. So, it's about a 15% water change monthly. The pump pulls water from the first chamber of my sump and returns to the last chamber. Doing automated, semi-continuous water changes isn't quite as gallon-for-gallon efficient as doing occasional ones (given that each change is removing a small part of the prior new water) but the differences are quite minimal.


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Author Profile: Simon Ellis or ca1ore on the forum.

Simon has over 20 years of experience with saltwater aquariums. He has experienced first-hand the changes in technology through the years, and is happy to share his vast knowledge with us here. Simon will be featured in a Profile of a Reef Aquarist coming up soon.