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The Conscientious Reef Aquarist

Tips for Reef Tank Water Success


by Bob Fenner


“All is water” goes the first record of human writing (linear B, Minoan); and this is indeed a true statement. Whether one interprets this simple statement as to the nature of reality or our more mundane efforts at marine aquarium keeping, it bears repeating that all definitely begins with the water, and can also end badly with it.

            Starting with high quality source water, carefully choosing, mixing synthetic seawater, proper storage, and monitoring are simple, yet extremely important matters. Herein are the highlights of what you can and should do to assure good quality water for your captive reef systems.

Source Water Quality Assurance:
            Unless you’ve been living under the proverbial rock, you’re doubtless aware of the growing scarcity of “good potable water” most everywhere; including in the United States. Times were that I and many other ornamental aquatics writers, scientists and practitioners advocated the use of “plain tap”, stating that “if it’s good enough for your potable purposes, it’s likely fine for your salt water aquariums”. That was then; this is now… a time of diminishing source water quality.
            Likely using most tap/mains water for mixing synthetic salt mix for fish only, and fish with live rock (sans “corals”) is still fine for the majority of people, places, but this is not the case for a growing number of localities where folks keep reef systems. The standard mantra for reef water quality is the less unknowns and contaminants the better… hence the perceived and real need for new tapwater treatment.
            Treatment for folks who know that their source water is fine chemically may just involve the use of a dechloraminator, a commercial product to remove chlorine/chloramine sanitizer that’s been introduced by their municipality to render it safe microbiologically.
            IF you have no inclination or ability to decipher your water provider’s analysis of the water they supply to you, or doubts still regarding its suitability, you will want to look into more involved water treatment methods. On the low end technology wise are the use of contactors; some very low-volume/production that “make” a few gallons per day by having a pressurized or not tap source attached to their contactor body and treated water dripped out the finish end. A larger version of this approach, and very useful for heavy users (hundreds or more gallons per day) is Poly-Bio-Marine’s (
http://www.poly-bio-marine.com/) Kold Ster-il filter.
            Beyond this unit and more refining still are various makes/models of reverse osmosis (RO) units that provide “mostly water” by excluding solids, gasses, other liquids. RO units are by and large the most practical, useful and therefore popular means of providing desired quality and quantity of known/good quality water for hobbyists and retailers. To mention it, there is a further filtering possibility, De-ionization (DI) and even a combination of DI w/ RO (RODI)… Suffice it to state that RO alone removes 99.99 plus percent of all alone.

Salt Mix Selection

            There are actual, measurable differences in salt mix formulations and quality; not least of which the issue of inconsistency has been a major flaw with some manufacturers. Do your duty here to look about, consider the input of other actual users (hobbyists), and not simply rely on the at-times misleading claims of various makers. Do seek out recent, up-to-date recommendations here as brands do come and go.
            Are “reef grade” mixes (often w/ simply boosted biomineral content) worth their extra cost? This really depends on what else you have supplement practice wise, use or not of calcium reactor et al. gear that might make up for a perceived need for more Calcium, Magnesium.
            What about savings in cost by bulk buying? Large buckets (150-200 gallon), 3 50’s per box, even club-split pallet purchases can really save money; and other than opportunity costs of putting your money up front and storage, there is no reason not to make such an investment. Some folks worry re “clumping” (salt mixes are hygroscopic), but even clumped up salt mix is fine to use, will dissolve completely over time.

Synthetic Mixing/Storing

            Though some manufacturers of synthetic salt mixes provide instructions for simply mixing and using their products right away, I strongly encourage you to instead pre-mix and store new water ahead of time for your change outs. Newly mixed salt you’ll notice has a sharp smell to it, and if you mix it by hand, it feels warm and a bit slimy… the warmth is the exothermic physical reactions of the salts going into solution, and the sliminess is mostly your skin dissolving from exposure to high pH…
            Pre-mixing and storing allows for all the components of the salt mix to dissolve completely and come to a homeostatic consistency. By recirculating and heating such water in a dedicated chemically inert container you also have the assuredness of readily-usable water should there be an emergency need, such as wanting to set up an isolation, quarantine or treatment tank.
            My all-time favorite containers for stored water are the Rubbermaid Brute line, replete w/ sturdy covers and wheeled dollies if you’d like. These polyethylene tools are tough and long-lasting. The submersible pump mentioned you can use for both dissolving new mix as well as pumping to your main/display tank.

Seawater System Maintenance: (including testing)

Yes; this topic could easily fill a book length tome on its own. Straight off, I want to make it clear that regardless of having and using the very best test gear, there is nothing better, more important than your observation of your livestock to make known what your reef water quality is, and alert you to the possible need to alter something.               
           For reef systems, there are numerous tests, measures one can choose to perform when first setting up; but for ongoing systems, these can be quite few. Unless one sees a real need, weekly monitoring of specific gravity, calcium, magnesium and alkalinity are all I do; yes, not pH necessarily. I rely on all systems of size to be stable with simple partial water changes to dilute metabolites and bolster alkaline earth concentrations (including a smidgen of Strontium) and alkaline reserve with a measured “pinch” of either dried or liquid two-part additives. This and a “squirt” of iodide-ate are all I regularly add. On very large systems I’m a decided fan of calcium reactor and ozone use (and RedOx measure).
          There are “gear heads” amongst us for sure; with as much invested in electronic probes, pumps and alarms… These tools can be useful but should not be relied on alone to monitor and administer all aspects of water quality. More biology, and less technology is still my creed.
          Are you surprised at my lack of automated top off use for evaporation? Don’t be. My systems are nearly completely covered on top, greatly reducing the need to add water more frequently than the once a week partial change outs. “Your mileage may vary”, so I would note the usual water level in your system and have “just water” handy to top off periodically.

            I am very aware of the naysayers here that eschew doing water changes… Some others vehemently assert that there’s no need to do such removal of old and replacement with new water. Rest-assured, there is NO simpler, safer and assured method to preserving water quality than frequent partial water changes. By regularly removing a portion of the water, best by vacuuming part of the substrate, you’re diluting accumulating wastes, precluding “Dead Sea syndrome”, and renewing needed macro- and micro-elements.
            Further, if you’re faced with an inexplicable issue of livestock health or loss, when, where in doubt, change some large (25 percent, perhaps more) amount of your system water. For sure you want to do what tests you can, check all your gear… but if/when all else seems fine, remember the value of dilution, re-centering your water quality back towards “new”.

About Natural Seawater (vs. Synthetic):

            Using “the real thing” should be mentioned in an article that even briefly covers the topic of reef aquarium water quality. Some might well be tempted to use natural seawater, as it IS what the life we keep originates in; but I assure you, the unnatural environments we control (aquariums) are better served by synthetic mixes. The latter have no issues of pests, parasites and pollution. And for folks that think or hope to be saving money; do remember to figure in the cost of hauling seawater, its longer storage and needed treatment. Phony/synthetic saltwater is more convenient, longer-lasting in terms of sustaining life and not yellowing, and less expensive overall. It’s not lost on me that the biggest public aquariums (e.g. Atlanta, Baltimore/New England), even ones near to the ocean use salt mix instead of real seawater.
          If you’re still not convinced that synthetic is better than natural for aquarium use, I want to make sure that you’ve been warned to look into others accounts of trouble with the real thing.


“It’s the water” goes an olde ad slogan for Olympia Beer (of Tumwater, WA) “…and a lot more”. Certainly your starting water quality is the beginning of success, or struggles in the reef aquarium interest. If you begin with water issues, or add to poor water quality, all will work against you: livestock health, poor appearance, pest algae issues and more.

Marylou: Some possible pix (make it known if these are fine and I’ll send full size to you… either FTP, Pando, Dropbox or simple email)


Marine Angels are amongst the more sensitive fishes to challenges of diminished water quality. Here an adult Pomacanthus semicirculatus in Fiji.

Look to your livestock’s change in behavior, colour for first indications of issues with your water quality. Here a healthy Pseudanthias squamipinnis male displaying in the Red Sea.

More often, sessile invertebrates will show signs of poor water quality distress ahead of your fishes. Bleaching in Cnidarians/Corals is common. Here an unbleached specimen of Heteractis crispa in Raja Ampat.

Calcium reactors, once set up and running properly, are the easiest, safest and sure means of providing alkaline earth minerals and alkalinity for reef systems. Here an Aqua C unit.

I’ve been diving on many reefs, and never encountered meters, dosers or monitors to assure water quality. Here a mix of mainly Sea Squirts on a Sea Fan in Fiji

The same considerations for tropical reef aquarium water quality pertain to cold water marine systems. Here a nice stand of the brown kelp/algae Macrocystis pyrifera off San Diego, CA

Natural seawater, as opposed to synthetic, can be made to work (of course), but it “lasts” not nearly as long and may pose real trouble in terms of hitchhiking pests and parasites. Here a native scene off Sharm ‘l Sheik in Egypt’s Red Sea

Commercial and hobbyist aquaculturists take the KISS (Keep It Simple Stupid) course by and large in providing and maintaining good water quality. Through the use of RO water, premium salt mix, and a routine of easy supplementation
Here at Anthony Calfo’s Xeniid farm in PA


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