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Related Articles: FOWLR Systems Plus; Live Rock, Fishes & Hardy Invertebrate Biotopes That Thrive Together by Bob Fenner, Marine Planning, Getting Started with a Marine Tank By Adam Blundell, MS, Fish-Only Marine Set-up, Reef Systems, Coldwater Systems, Small Systems, Large Systems, Plumbing Marine SystemsRefugiumsMoving AquariumsMarine Biotope, Marine LandscapingFishwatcher's Guides

/The Conscientious Marine Aquarist

 Fishes & Invertebrates aka FOWLR Marine Set-ups

Some fishes, like the large-mouthed scorpaenids, will suck up most any edible invertebrate.

By Bob Fenner

Small Marine Aquariums
Book 1: Invertebrates, Algae
New Print and eBook on Amazon:
by Robert (Bob) Fenner
Small Marine Aquariums
ook 2: Fishes
New Print and eBook on Amazon: by Robert (Bob) Fenner
Small Marine Aquariums Book 3: Systems
New Print and eBook on Amazon:
by Robert (Bob) Fenner

It's hard to make wide-sweeping statements about the fishes as a "super-group". Some species are timid, some are real bruisers. There are fishes that can survive most any treatment, while I've seen other's die of fright just from sticking a net in their tank. Pelagic Triggerfishes may be caught using orange peels or paper towels thrown over the side of the boat as "bait"; assorted butterflyfishes have never been observed to eat in captivity... Yes, the fishes are a diverse assemblage.

They pale in comparison to the non-fishes we call invertebrates. These come as attached, swimming, burrowing, crawling, internal and external symbionts in/on all marine environments, from the surface to below abysmal depths. Some are incredibly tough aquarium specimens, others die if simply lifted from the water. Many are incredibly beautiful.

Very happily, the quality and selection of invertebrate animal life offered to marine hobbyists is vastly improved, and improving over years' past. Enhanced collection, transport and even culture (e.g. giant clams, algae, corals) has greatly expanded what's available and it's likelihood of survival.

In this article we will discover the ways that a marine system that includes invertebrates differs from the archetypal fish-only or "general" marine set-ups. The same concerns as to acquisition, proper acclimation, order of introduction and compatibility apply as for "fish systems". What is really different is the trend for increasing intolerance for "poor" water quality and variance.

Invertebrates as a whole do not put up with near as much "metabolite poisoning" from any source, including themselves, nor fluctuations in specific gravity, temperature and such compared with fishes.

One useful way of reminding yourself of their relative "touchiness" is to consider how much less mobile many invertebrates are compared with fishes. Most non-fishes can either move away from "undesirable" circumstances (thermal change, predators, pollution...) slowly or not at all compared with finned animals. What will they do in your system if conditions are adverse? Die.

The need for diligent testing and maintenance of improved filtration & circulation, temperature control, overall environmental quality and stability is greater in dealing with invertebrates. You can see the logic in practicing first with a "fish-only" marine set-up and thoroughly studying-up before moving into keeping non-fishes.

The Animals:

Though there are many times more marine invertebrates than fishes, only a few dozen species are generally available at any one time. This situation reflects what is the current state of demand, not supply. Any snorkel/dive experience, real or virtual (television, books, etc.) reveals the fantastic wealth of invertebrate life. Increasing commercial demand will spur collection, study, writing, and success with marine invertebrate keeping.

For our discussion, invertebrates include nudibranchs, anemones, sponges, starfish, clams, gorgonians,... and so many more that it's better to define them by what we'll leave out. Let's consider and leave out live rock and sand, the macro-algae, true or stony corals, leather et alia coral and coral-related organisms as part of the domain of "reef systems".

Equipment & Use:

The gear available for "invertebrate" (or fish & non-fish) systems is extensive, and sometimes expensive. What is actually necessary beyond "standard" marine, "fish-tank" components and their arrangement is more of a matter of degree, than kind with one possible exception; lighting.

You still need as large a system as you can lay hands on, all the elements of filtration (biological, mechanical, protein skimming), heating, etc., but now their sizing/capacity and operation must be more stringent.

Maybe a comparison with "American" cars and a fancy-schmancy sports import will reinforce this idea. You know that ignoring the import's maintenance schedule, not keeping the finish clean, etcetera is courting disaster; it just has much narrower tolerances than fish-only/U.S. autos. Invertebrates by and large will not put-up with rapid or extreme changes in their routines or water quality. Keep to a schedule of checking and maintenance, the same as that Ferrari, and everything will be fine.

Lighting is the one possible "wild-card" with invertebrates; some "spine-less animals" bear photosynthetic algae that require proper illumination, and almost all are sensitive to irregularities in light duration, quality, and sometimes intensity. I encourage you to read as much on lighting as you can. Know that many non-fish appreciate full-spectrum (fluorescent) illumination, provided in a predictable schedule. Use a timer to control your lights for sure.

Covers. You may have gotten away without a close-fitting hood with freshwater or fish-only marine systems, but you are warned; many marine invertebrates can/will "exit stage left" though they might (for now) seem incapable. Besides, you don't want to hassle with water/heat/salinity changes from having an incompletely covered system.

Substrate, aka gravel; size, type and depth may now be important. You might have left it out completely with just having fishes, but what if Puka, coral sand, dolomitious material is necessary for an invertebrate's eating, growth, housing, hiding...? Studying is your self-made guide to success.


Remember the procedure adopted for fish-only systems? Here you want to do the same things; with one change. Wait up on non-fishes until cycling bacteria are settled in. That is, after a number of your fishes (if you're using them) have been introduced, without any detectable levels of ammonia and nitrite following, the system is ready for you to start placing your invertebrate life.

The same acclimation, quarantine and systematic approach is taken to steadily add numbers and metabolic activity to the system.

Why use the fishes to break in the tank? Simple; they are tougher than most non-fishes. Also, not so simply, their actions and time going by do a great deal of good in terms of "aging" the water.

What if you're going to have a largely, or total invert. system, without much or any fish life? For one, utilize animals that can weather a "break-in" period; and secondly, take care in preparing your synthetic saltwater (if not using natural). The fabricated water should ideally be mixed a good week in advance, allowing for out-gassing, elimination of potable sanitizer... If you must mix and use a synthetic mix within a short while, at least make sure it is totally dissolved and treat it with a commercial dechloraminator.

Protein skimming; when to turn it on? After the fish ammonia-nitrite cycling is over, before the invertebrates are put in.


The social structure of invertebrates with each other and fishes presents many potential problems. Interactions that result in consumption may be the least of your worries; many invertebrates (like the cucumbers called sea apples) have chemical and physical defense mechanisms that may take out your whole tank if they're disturbed. Read through the invertebrate sections in references before purchasing.

As a helpful suggestion, consider mixing animals in a biotope that hail from the same area; especially a shallow water environment. Another useful tool is a clear, plastic screw-lid container that has holes drilled or melted into it to allow circulation. A new individual may be floated, or set on the bottom where it can become "familiar" chemically and visually with tankmates for a while, without each being able to get to the other physically.

Miscellaneous; Density, Supplements, Feeding, Disease

Carrying capacity  

For systems with invertebrates is difficult to gauge. Sure, with a super-duper filtration system, outfitted with meters, dosers, sumps and pumps galore, you can "get away" with piling in life chock-a-block; but at what cost and safety margin? What would happen if the power were off for an hour, a day? What if "something" died?

I don't feel comfortable offering any rule of thumb, or formula that would encompass all the variables; what types of life, amounts, feeding, filtration, buffering mechanisms... (you can imagine) that would be meaningful to determining carrying capacity. What I will write is that under-crowding and observing your livestock closely are requisites for satisfaction.


You are encouraged to promote the growth of green micro- and macro-algae with your invertebrates (and fishes) to the extent that it detracts from your enjoyment (covering the front viewing panel). Having live algae in the system does a myriad of good things beyond being a hallmark of a healthy system. The algae provide food, oxygen, and may take up considerable amounts of undesirable nutrient/wastes. Besides, they are beautiful. If you must, for appearances sake, clean algae away from only part of your tank and decor at a time; but remember, "cleanliness is not sterility."


I will "reverse" myself on the position of utilizing chemical adjuncts in the case of "crowded" (what's that?) invertebrate systems. If you have more than a few crustaceans and clams, your system may very well benefit from the weekly addition of trace elements, vitamins and pH buffer. For "less-crowded" set-ups, weekly partial water changes do just fine. How can you tell which "crowded" category you're in? Try adding these materials and see if they do your sea life any good; it won't hurt anything but your wallet to experiment.


This is a huge possibility to write on and on about how invertebrates employ every mode of gathering and utilizing all known foodstuffs. Suffice it to state that the invertebrates offered for sale to you have any number of needs/demands that must be known, met and understood as their part of a system's community. You'll have to assure that everybody is getting fed adequately, otherwise they will find someone else to nibble on.


Is another "monster" category. As with fishes, the majority of invertebrate problems are due to poor water quality and lack of nutrition. What is known currently of their biological diseases could fill several large volumes; what is known that is of use to aquarists in the way of their infectious and parasitic diseases would fit in your pocket.

Know what a healthy, vigorous animal looks like before buying and do your best to meet it's physical and "psychological" needs. If an invertebrate stops feeding, shows unusual behavior, shows "spotty" or loss of color, it is best to remove and isolate it in your quarantine system. Never put treatment chemicals in the main system, and never treat invertebrates with copper compounds.


For invertebrates or "mixed" tanks, upkeep is similar to that of other types of marine systems with added emphasis on regular testing and stability.

Basic water quality parameters that must be monitored are specific gravity, temperature, pH and ammonia/nitrite, and possibly nitrate. Desirable values (very generally for all groups) are 1.022-1.026 for spg (30-35 ppt salinity), 75-80 degrees F. (unless it's a cold/cool water system), 8.0-8.4 pH, no detectable ammonia or nitrite, and a few tens ppm of nitrate.

Talk about feeling shaky! I know that these are wide ranges, but they'll suffice for the intent and coverage here. What you want to shoot for is keeping your water quality steady within these "limits". Topping off, weekly checking of parameters, and frequent partial water changes are better than all the fancy gear in the world on an otherwise ignored system.


Considering how little there is written about marine invertebrates in the hobby press, you'd assume that such organisms are rare, or impossible to keep. Such is not the case; there's is an even wider range than the fishes in terms of invertebrate tolerance, compatibility and interesting behavior.

As with marine systems housing only fishes, attention must be paid to meeting the living and community requirements of non-fishes. They are less forgiving than most fish groups and intolerant of chemical abuse and neglect.

Addendum to FOWLR 2.0

<”Short sidebar on live rock: types available, how to buy, how much per gallon of tank volume, etc.  ALSO: a bit on live sand and coral sand options.”>

Live Rock:

Types available: Choices come down to real rock (collected in the wild) from Florida or the South Pacific (Fiji, Indonesia…) and man-made artificial rock that has been inoculated via submersion in the ocean.
The Florida rock is much more dense, and bearing life of the trop. West Atlantic. It’s about the same money per pound or box as the S. Pacific choices, and though it will do fine being used with livestock from other seas, I only favor its use when having a Caribbean biotope.

            The South Pacific rock is less dense, so for looks, you don’t need as much, and it typically has more diverse and abundant life present than the FLA product. So, for me, I prefer it over the Florida for most applications.

How to buy:  Volume is your friend; if at all practical, buy by the box or larger stated weight break. Ask your fellow reefers, club members re going in on a group buy, and don’t leave out the possibility of co-shipping or special ordering your rock with your Local Fish Store (LFS). They can get a better deal and make it easier for you as well; by piggy-backing your box or three with their shipment. You may have to pay up front and do all the processing/curing on your own, but the savings can be significant

How much for your set up? In the olde days of “rock walls” folks used to plunk down the big bucks to buy 1.5-2 pounds per gallon or so to get enough rock. Functionally and aesthetically this is too much. I would opt for using maybe half a pound per gallon or so (you can always add more later) to build bommies, or lean-to corner structures, caves, overhangs, leaving much of the center of the tank as open space.

Live Sand:

Types available: Here again there are two ways you can go: Au naturel or bagged/commercial. Quite a few outfits sell the real thing… live collected or perhaps more often, “made on site”, by exposing rinsed, sterile sand to micro- and macro-organisms by placing live rock over it. You can do the same if you prefer the latter. The bagged product just hosts purposeful microorganisms; and here the company CaribSea scores high with their Arag-Alive line of substrates. There are other makes, but CaribSea has the most consistent, greatest selection; adding other beneficial microbes to hasten the establishment of nutrient cycling.

How to buy: As mentioned with live rock, quantity buys are the route to go if purchasing larger amounts of live stand. If you’re utilizing hundreds of pounds and have the time, again, I would make my own, inoculating it by seeding from fresher, though cured live rock placed above it.

How much for your set up? Some folks go the route of buying all their sand as live; I consider this over the top; unnecessary. If going the bagged way, spreading up to a half inch on the top will get you about all you can hope for.

Coral Sand:

Types available: This material is highly variable; in grade, variability in same and composition. There are still occasions when/where “sand box” coral sand can be acquired on the cheap; but I would rather endorse the use of processed for aquarium use. The purposeful sand has been more thoughtfully cleaned and screened for impurities in my experience.

Regarding grade: Grain size can be important… for engendering anaerobic processes (e.g. denitrification), aiding sifting organisms, burrowing… and providing more surface area per volume (hence more solubility, dissolving for adding alkalinity and alkaline earths). This being stated, I would not go with too-fine a grade; about 1mm diameter is good for most all aquarium purposes; fine enough for aerobic and not microbe culture, about right surface area for dissolving, and large enough to stay on the bottom, not making dust clouds from pump circulation and livestock movement.

How to buy: as per live sand above.

How much for per your set up? Depends on what you want to do… some folks eschew use of substrate period, preferring to go “bare bottom”. For some others, having a part of an inch is what they’re liking for looks. For me, I am a fan of having as much substrate as possible, practical, having an active Deep Sand Bed (DSB) in the main display tank as well as live sumps (refugiums). This means a few inches of sand; depending on the configuration of your tank, this might be 2, 3 or more pounds per gallon.


Bibliography/Further Reading:

Blasiola, George C. 1988. Marine invertebrate health. FAMA 4/88.

Dakin, Nick. 1992. Starting with invertebrates. Aquarist and Pondkeeper 12/92.

Donovan, Paul. 1992. Healthy invertebrates. FAMA 10/92.

Garibaldi, Louis. 1975. No bones about it. Marine Aquarist 6(1):75.

Giwojna, Pete. 1988. The invertebrate tank: a coral jungle in your living room. TFH 4/88.

Hemdal, Jay. 1988. Saltwater fish and invertebrates; mixing marine fish and invertebrates can be done, but only with careful planning. AFM 12/88.

Hunziker, Raymond E. 1986. The marine aquarium made easy, part 2: invertebrates. TFH 11/86.

Kloth, Thomas C. & Michael F. McMaster. 1978. Invertebrates, parts 1-5. FAMA 3,4/78.

Lamberton, Ken. 1992. Starting with invertebrates: your first marine aquarium. TFH 10/92.

Parker, Nancy J. 1973. TLC- Rx for an invertebrate community. Marine Aquarist 4(2):73.

Robitaille Ron. 1982. Feeding invertebrates. FAMA 9/82.

Small Marine Aquariums
Book 1: Invertebrates, Algae
New Print and eBook on Amazon:
by Robert (Bob) Fenner
Small Marine Aquariums
ook 2: Fishes
New Print and eBook on Amazon: by Robert (Bob) Fenner
Small Marine Aquariums Book 3: Systems
New Print and eBook on Amazon:
by Robert (Bob) Fenner
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