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Related Articles: Marine Maintenance, Water Changes/Changing, The "Perfect" Water Change Regimen?, Treating Tapwater for Marine Aquarium Use, Major/Minor Seawater Constituents, Seawater, Natural or Synthetic?, Understanding Calcium & Alkalinity,

/The Conscientious Marine Aquarist

Marine Aquarium Water Quality

By Bob Fenner

Livestock are the best indicators of water quality. Observe yours closely.

What is this ideal, this oxymoron, this mythical beast "Water Quality"?

Asked to name the 'secret' to successfully keeping marines, what would you say? Buying the 'right' specimens? Proper acclimation, feeding? All these are critically important; as is keeping parasitic and infectious diseases at bay.

You may well recall, the third triad in our model of factors determining the well-being of any system is suitability of the environment. For the majority of situations/circumstances we are talking about water quality. Of the controllable variables of aquariculture, it is the most important. Let's make this perfectly clear; everything about the health of your system is tied to water quality. If your fishes appear ill, do not first suspect disease, refrain from changing their food, light, or anything else; check the quality of your water. I swear more aquatic life has been 'saved' by moving to new water, or executing a massive water change, than the use of all medications combined.

To put this concept in more succinct terms: Nearly all livestock problems start and end with the appropriateness of their liquid medium.

Let's work our way into a definition of what good water quality is and how it is best approximated. You won't have to become a chemist or physicist, I promise.

An Ideal Set-up:

Take a gander at the photographs of public aquariums offered in this magazine. How do they keep the water in their tanks so clean and clear? I know what you're thinking; "They must have super-filtration systems, with digital dosimeters like a nuclear power plant, exotic towers, and a full-time scientific staff." "Bob the Fishman lied; I am going to have to become an engineer". Well, guess what, that gin-clear water is often due to a sand filter, the beach. Some of these public aquariums dig saltwater wells and pump up the seawater that percolates to it through the surrounding porous rock. Good deal. Their "open circuit" and "semi-open" (recirculated) systems return the barely used natural water back to the adjacent ocean.

We're not quite so fortunate with our "closed", recirculating units. Our water starts out as good as we can make it and degrades from there, chemically and physically. The use of various filter modes, additives and maintenance only serves to slow down the pace; water quality dis-improves. Be aware, but don't let this bum you out. The majority of organisms available to the hobby have a wide tolerance and are adaptable to initial and aged water conditions.

Natural Seawater 

Is not used by most aquarists. Look in the hobby magazines; you don't see many advertisements promoting gear for manipulating real seawater. Synthetics are almost universally employed; huge public aquaria even use them. For instance the "new" National Aquarium @ Baltimore. Even though it's right on the Bay, they mix up and recirculate hundreds of thousands of gallons of synthetic seawater.

Discussion and arguments for natural/synthetic saltwater I've covered before (see Bibliography). Let's focus our attention here on artificial mixes; what most everyone employs.

It's the Water, & A Lot More:

The United States has gone from agricultural, to manufacturing, to services and through the eighties well into the information age. Forget about investing in the technical highway; get with a real booming field> Saltwater Mixes. I wish you and I got to have the money all the manufactures spend advertising every month in the hobby magazines. Talk about a growth industry.

Is there really that much difference (besides price) amongst all the brands? Yes & No. Some are more "pure" in that they are composed to a greater degree from "technical" and "reagent" grade constituents (yes, I used to teach chemistry and physics). Others can portend they are more "complete" in that they specifically have tested (more) vigorously for and/or added more elements and compounds mimicking "real" seawater. Admittedly they vary in initial pH, alkaline-reserve, re-dox, etc.; but ostensibly they all will/do support most forms of captive marine life. Other factors in artificial seawater-making loom large in consideration of "quality".

Some Background

The composition of seawater in it's various salts (about 35 parts per thousand), minerals, metals... is often presented as being of rigid, and homogeneous constitution throughout the world's oceans. And the wildlife in it being of narrow tolerance of change in this 'holy grail' consistent medium.

This is only part of a/the big picture as regards the waters our livestock hail from. Almost all are collected from places that are opportune to humans, not surprisingly. They are typically shallow water, coastal, near population (polluted) centers, that are subjected to varying specific gravity, run-off, sewage, wave action induced pH fluctuations... What's more, all living things show a broader-narrower tolerance /range to environmental conditions.

Hence our chances at successfully meeting their needs in artificial media.

The principal ingredient, by weight and volume in a marine system is... H2O. Your tap water has much more to it then Hydrogen and Oxygen. Ordinary mains water sports dissolved and suspended gases, solids, other liquids, remnants of, and organic life; and a sanitizer (usually chloramine). Here in Southern California we regularly have several hundred parts per million (ppm) of total dissolved solids (TDS) in our tap.

Does all this glop (non-scientific term) pose real problems for an earnest marine aquarist? No, in all honesty, it's minor spuds (small potatoes) compared with all the other contributing factors affecting the make-up of your system's water.

Hear me out. The E.P.A., among other agencies, mandates just how much of several (from the Middle English, meaning 'many') chemical and biological species are allowable in potable water. For instance, tap must have a concentration of less than 1.0 ppm total Nitrate (NO3). Further influences? Have you thought of the ongoing effects from dissolving substrates, rock, decor, feeding (one ounce of food in one million ounces of water would be 1 ppm), biological processes going on in your closed system? And what about the interactions between all this and the salts and more you add to the water?

If you've grown fond of lugging bottled water, utilizing reverse-osmosis, or even distilled water, more power to you. But let's keep all this in perspective. The bulk of undesirable "extras" in tap water can be either ignored or easily removed either through an in-line chemical contactor" (e.g. Aquarium Pharmaceutical's Tap Water Purifier (tm)) or commercially produced conditioners.

Not to disparage the use of more "purified" water out of hand/proportion; my point is that compared with other contributing factors, for marine systems, ordinary treated tapwater is not a major source of concern in terms of added nutrient, pollutants, metals... Freshwater biotopes (e.g. wild discus, some killies) that appreciate far less in their water are a different matter.

Keeping Water Quality High: Filtration 

Some of the general techniques used to preserve water quality will introduce here; and discuss them more fully in upcoming issues.

Biological Filtration: is the sum-total of interactions between the micro- (one's you can't see with the naked eye) and macro- (one's you can) life, rendering less-noxious the waste-production of the latter. 'Sterile' new marine systems don't stay that way for long. Colonizing microbes come in via the air, water, items that find their way into the system, intentionally or not. Eventually (after a few weeks) without adding desirable varieties, beneficial microbes become established in a system sufficient to readily process livestock wastes.

These processes are expedited by use of undergravel filtration, wet-dry techniques, live-rock, fluidized bed, nitrate et al. scrubbers...

Chemical Filtrants: like activated carbon and specialized resins are used to remove dissolved organics. They do also remove trace materials you want in the system, but this is an agreeable trade-off.

Mechanical Means: of removing particulates; power filters, diatomaceous earth, cartridge types, etc. take out suspended matter aiding their removal, digestion by microbes.

Air-stripping, aka Protein skimming is a given for me; all marine systems benefit from their use and should be outfitted with them. Where properly built (a rarity) and used, skimming is supreme at improving water quality via fractional removal of organics.

Ozone the tri-atomic (O3) form of Oxygen, added through a skimmer or by itself raises reduction oxidation potential, adds to conversion or organics.

Ultraviolet Sterilization is of some, but limited value with other filtration and system maintenance considerations taken into account. U-V's are useful in reducing free-floating microbe populations and their biological effects, nominally raising re-dox, oxygen and ozone levels.

To recap; it is my opinion that marine systems must be outfitted first with working Biological Filtration, then with a protein skimmer, with or without an ozonizer. Ultraviolet is and should be a last concern.

Loading otherwise known as stocking, crowding a marine system with livestock is difficult to quantify, and seemingly impossible to control for aquarists. Obviously, the less "fixed-carbon" (life), concomitant addition as food, the minimized effects of induced-pollution, metabolite build-up... So small is beautiful in stocking your system. Public aquaria allow as little as a few ounces of livestock per hundred gallons of system water. My guideline is any more than a cubic inch of any given mix of specimens per five gallons is pushing it, asking for increased maintenance, and trouble.

Water Changes are the single most important means you have to reduce the effects of captive containment, ultimate shift, loss of water quality. Diluting ill-effects, adding "trace" materials from new seawater should be done on a regular, consistent time schedule. Do not be sold on any given technology that purports to make "water changing unnecessary". Frequent, partial water changes are the least expensive, most effective way to ensure and sustain aquariums successfully; period.

This being written (and believed), remember 'cleanliness is not sterility'; there are beneficial substances produced by life processes. You want to vacuum clean only a portion of a system at any time. Depending of course on your systems' size, configuration, particulars of filtration, circulation, foods/feeding... probably ten to twenty percent every few weeks.

Supplements: The relative merits of additives will be covered later in a piece titled Adjuncts to Water Quality

Test Gear: How can you tell when and to what degree your efforts are necessary or productive? Hydrometers to measure specific gravity, test kits of myriad types can be useful tools, "windows" for looking into changing conditions in your water quality.

In Summary:

It is easy to see how easily our water quality degrades in such small, overcrowded, often underfed captive systems. It can be bewildering to get too involved in understanding, or worse, driving one aspect of "water quality" without concomitant awareness of how that change affects other aspects of chemistry, physics and biology of your system. Fear not, as most appropriate livestock that has been collected and held properly is quite tough and resistant to the vicissitudes of aquarium confinement.

Do learn the consequences of the major testable criteria of water quality, avail yourself of the gear for evaluation (test kits), and be fastidiously regular in your maintenance; in particular frequent, partial water changes.


Anon. 1974. Saltwater quality. Aquarium Digest International 2:4/74.

Bidwell, Joseph P. 1976. Water quality and the bioassay. Marine Aquarist 7:7/76.

Campbell, Douglas G. Water quality in the marine system, parts I & II. FAMA 6,7/95.

Dawes, John. 1988. Water quality in marine systems. Pets Supplies Marketing 8/88.

Emmens, C.W. 1989. Water quality in the marine aquarium. FAMA 8/89.

Fenner, Bob. 1989. Frequent partial water changes. FAMA 4/89.

Fenner, Bob. 1991. Seawater, natural or synthetic? (Which way to go?). FAMA 9/91.

Glodek, Garrett. 1993. The properties of seawater. FAMA 2/93.

King, John, M. 1972. Marine aquariums are NOT miniature oceans. Marine Aquarist 3(4)/72.

Smit, George. 1989. The water quality factor in marine aquariums, parts 1 & 2. FAMA 1,3/89.

Sprung, Julian. 1996. Water quality: Saltwater; more than just numbers. AFM 6/96.

Thiel, Albert J. 1993. Introduction to water quality. FAMA 3/93


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