Starting With Invertebrates

Soft CoralThere's no doubt about it, a well arranged coral invertebrate aquarium can be one of the most impressive and satisfying sights you are likely to witness within the fishkeeping hobby. People seem to be drawn like a magnet to its exotic beauty and a certain disbelief that something so defying adequate description could possibly be real! The romanticism and awe-inspiring beauty associated with coral reefs has been witnessed to some degree by nearly everyone, courtesy of the television or cinema. The urge to acquire a piece of coral reef 'real estate' for the lounge can be very strong indeed, leading to uncontrollable weekend spending sprees, high hopes and good intentions. Not, however, the best recipe for a successful marine aquarium I am sorry to say!

Stable Conditions

With few exceptions, invertebrates are significantly more sensitive than the many fish commonly available to the marine aquarist and as a consequence, water quality needs to be maintained at a scrupulously high level. Sudden changes in pH, salinity, temperature, etc., are to be avoided at all costs and the aquarium should be reasonably well established to guarantee the stability required.

The Right Beginning - The Tank 

Taking into account the need for complete stability, it would be best to choose the largest aquarium possible; small aquaria are not very reliable in this respect and parameters can change rapidly causing a great deal of stress, leading to deterioration and death. The newcomer would do well to consider a minimum tank size of 36"x15"x18", giving a net gallonage of around 30 gallons and stable enough to support a good selection of invertebrates.

The Filter 

Having invested in an aquarium with a suitable volume, the next factor to consider is efficient filtration. The traditional method of undergravel filtration is perfectly acceptable for many invertebrates, especially when run in reverse-flow, but the addition of even a small trickle filter or fluidised bed can improve the quality of the water substantially. The Juabert and Berlin systems are also worth considering if the newcomer fully understands their mode of operation.

Trickle filters are popular with the marine fishkeeper because they are efficient, easy to maintain and keep the water quality particularly high. So, before investing in an undergravel system as a first and only option, it is worth looking at some of the many trickle filters on the market specifically designed for marine use.

Protein skimmers form an essential part of the system, extracting waste products before they can put an extra load on the biological bacteria. Indeed, some systems rely almost entirely on ultra-efficient venturi power skimmers supplemented with only minimal biological facilities.

Marine-grade activated carbon can be almost as desirable as the protein skimmer in its ability to adsorb unwanted toxins from the water. This can be fitted in a canister filter, external trickle filter or trickle filter sump and will need changing every two months. More advanced systems will include such items as oxygen reaction chambers, Kalkwasser dosing units, calcium reactors, denitrification units, UV sterilizers, ozone reactors and various other refinements, all of which may vary in their desirability but certainly not essential at the outset.


Many corals possess a symbiotic algae within their tissues called zooxanthellae. The well-being of this algae is essential to the survival of the animal and relies on high intensity lighting of the correct quality. Top of the list for most suitable lighting comes the metal halide (HQI) spotlamp. These, however, may prove beyond the pocket of most hobbyists as two or three lamps may be required to effectively illuminate a 5-6' tank. However, prices are falling all the time and the investment will be well worthwhile.

Fluorescent tube technology has advanced considerably in the last few years and it is now possible to have a thriving community of light-loving invertebrates supported by this form of lighting only. It is usually necessary to cram the hood with as many tubes as possible to achieve the high intensities required and this may amount to 4-6 full length tubes in an average aquarium.

Whilst mercury vapour lighting still has its supporters, it is limited as far as light quality is concerned and needs extra support at the blue end of the spectrum in the form of actinic lighting. Even then, the long term efficacy has been questioned by many advanced aquarists. It goes without saying (but I am going to say it anyway) that if light dependent invertebrates are not kept, then illumination largely becomes a matter of personal taste and creature comfort. For example, a lobster housed in a single species tank will require enough light to be able to observe the creature but not so much as to disturb its largely nocturnal nature. A photoperiod (lights on) of 12-14 hours each day will be necessary for most aquaria and may be operated by a timer switch for convenience.

Maintenance and Supplements

It is absolutely essential that regular water changes are carried out to re-vitalise the aquarium environment. Once a few changes are missed it becomes progressively more and more difficult to halt the decline in water quality. Use the purest water available, which may not always be tapwater (in fact, hardly ever!) that should be nitrate and phosphate-free. This may mean filtering the mains water through a nitrate removing filter cartridge, deioniser, or the best option, a reverse osmosis unit.

The salt mix should also be free of nitrates and phosphates for obvious reasons. Invertebrate aquaria may benefit from the addition of weekly supplements in the form of trace elements, vitamins and pH buffering compounds. Although many other additives are available these may not be necessary if proper water changes are undertaken as they largely act as a 'prop' for deteriorating water quality. If in doubt, decide if a particular supplement is applicable to your situation. For example, a strontium and molybdenum additive can help prevent hard corals detaching from their calcareous skeletons, but would obviously be unnecessary if hard corals are absent

It is worth noting that as tankwater evaporates, salinity rises and this may induce osmotic shock in some of the more sensitive invertebrates. An advanced osmolator will replace quantities as little as one teaspoonful of evaporated water continuously throughout the day. If this is not affordable, replace evaporated water very regularly - at least once every two days - using very pure fresh water. If poor quality tapwater is used there is a risk of a toxin build-up which can prove to be very troublesome in the long term.


Filter feeding is common in the world of invertebrates and the most difficult form of feeding to accommodate in the aquarium environment as liquid foods can soon very easily foul the filtration system, putting the lives of all animals at risk. If liquid foods are felt absolutely necessary, use them sparingly indeed and if possible, substitute for slightly more natural live alternatives such as brineshrimp nauplli and rotifers. They are not difficult to culture and are readily taken by all filter feeders.

If fish share the same aquarium, the juices from their frozen foods can often act as a good liquid substitute and make any extra supplementary feeding, other than live, quite superfluous. Gross feeders are an altogether easier proposition. Anemones and related species, as well as most crustaceans will take measured portions of cockle, mussel, lancefish and squid on a one to two weekly basis. Whichever feeding method is called for, it is a wise policy to restrict quantities to an absolute minimum and present the food in a structured way.

Test Kits 

Accurate water testing is indispensable and a good range for the invertebrate aquarium would include :- ammonia, nitrite, temperature, nitrate, pH, copper, s.g., dissolved oxygen, phosphate, calcium, alkalinity and KH. Regular testing will help to spot deficiencies or the rise in potentially dangerous toxins at an early stage and enable swift remedial action to prevent the loss of valuable livestock.

Aquarium Diary

I would recommend that all marine aquarists and invertebrate keepers in particular, keep a diary whereby all test results, water changes, additions to stock, disasters, etc., can be recorded throughout the life of the aquarium. The memory is very unreliable and a diary can be invaluable in this respect.


Each invertebrate has its own degree of difficulty' and newcomers would be wise to avoid certain species that require an experienced hand. In broadly general terms, invertebrates can be categorised under three headings :

i) Easy - recommended for newcomers,

ii) Care Needed - best left until experience is gained,

iii) Difficult - species that require best possible conditions and/or feeding regimes and special understanding.

Here are some examples:-

i) EASY Most shrimps, star polyps crabs and lobsters. Leather Corals. Soft Corals. Pulse Corals Anemones Mushroom Polyps. Tubeworms. Brittle Starfish. Sea Urchins.

ii) CARE NEEDED Sponges. Sea Pens. Sea Whips. Anemones. Clams. Colonial Tubeworms. Octopuses. Starfish. Sea Squirts.

iii) DIFFICULT Dendronephthya sp. (Cauliflower Coral) Sea Fans. Jellyfish. Hard corals - e.g. Goniopora sp., Euphyllia sp., etc., and all those species with a calcareous skeleton. Cowries. Nudibranchs (Sea Slugs) Scallops. Oysters. Cuttlefish. Nautiluses. Crinoids Sea Cucumbers (including Sea Apples)

Some Tips

1) Corals do best when left undisturbed. constant rearrangement can be very unsettling, triggering premature deterioration and certainly not conducive to growth or multiplication.

2) Give corals a chance to spread to their true size by not overcrowding; many species have defence mechanisms designed to discourage or kill neighbours encroaching on their space.

3) The invertebrate aquarium cannot be stocked indefinitely. Stop before it looks overcrowded i.e. animals touching.

4) Avoid disturbance of the substrata especially around clams and other species that filter water.

5) Keep crustaceans regularly fed. Hungry specimens have been known to feast on other invertebrates in the absence of a suitable food source.

6) Understand the needs of an invertebrate before purchase. If these needs cannot be provided in full then don't buy it.

Skunk Clown in AnemoneFish For The Invertebrate Aquarium

The vast majority of aquarists will want to keep a selection of fish with their invertebrates (although this need not be looked upon as obligatory in any way). However, it would be prudent to list a few drawbacks with this strategy. Firstly, fish produce copious amounts of waste and this can badly affect the health of invertebrates in such a confined space. The option here is to keep fish stocks down to a very low level indeed 1" of fish to every 6 gallons nett after slowly stocking for one year. This is a formula that I have advocated for many years, and I stick by it.

Overstocking with fish is the commonest cause for the demise of invertebrates. In addition, fish are notoriously difficult to treat for diseases when invertebrates are present, as many fully effective medications, particularly copper, are lethal to them. Not all fish are compatible with invertebrates (or themselves) so care must be exercised. Fish must also be disease resistant and, needless to say, harmless to the invertebrates.

The following is a selection of commonly available species that have proved attractive and suitable inhabitants for the invertebrate aquarium:-

Anemonefish (all species) Firefish (all species) Mandarinfish. Psychedelic fish. Scooter Blenny. Blennies (most species) Dwarf Angels. Gobies (most species) Pseudochromis sp. Dwarf Wrasse. Wreckfish. Damselfish.


Never underestimate the usefulness of books. They can be an invaluable source of information and convenient guide to correct procedures. Constantly relying upon aquatic retailers can be confusing (not to say expensive!) as there is not always time to make an informed decision in a crowded store.

© Nick Dakin. May not be reproduced in part, or whole, without permission.