Many people believe that invertebrates are only for mini or micro-reef tanks. Not so. There are quite a few invertebrates that do well in non-reef tanks. However, not a lot of invertebrates should be attempted by inexperienced saltwater fish keepers. Below is a brief summary of the more hardy invertebrates available to aquarists.
Invertebrates are very sensitive to water quality. Signs of stress due to poor water quality will usually be exhibited first by invertebrates. Therefore, shrimps, anemones and other invertebrates should never
be used to cycle a tank. Moreover, you should never add an invertebrate to a diseased tank or a tank
which does not have stable water quality parameters (e.g., pH, temperature, etc.).
Other points to note. Shrimps need iodine to properly molt, as well as calcium . If you do not change water regularly (which you should), or if you do not feed live or frozen food frequently, then you may need to supplement your water with iodine. Without proper levels of iodine, shrimps will not molt properly and will most likely die. Also, copper kills invertebrates at much lower concentrations than fish. If you have ever used copper in your tank, DO NOT put invertebrates into the tank. You will never be able to adequately remove all the copper such that you can keep invertebrates alive and happy. Finally, crabs usually outgrow their shell sooner or later. Therefore, you will need to provide a new larger shell (they usually try a few out before sticking with one, so you will probably need at least a couple).
Fish and invertebrates together?
Many hobbyists desire to keep a mixed collection - with both fish and invertebrates in the same aquarium. While such a display can certainly be very beautiful (especially with symbiotic species like Anemones and Clown Fish), there can be problems involved. The most effective treatments for saltwater "ich" also kill invertebrates.
Apparently, the cell structures are similar enough between parasites and invertebrates that the reactions to chemicals are quite the same. Since the treatment/removal time for "ich" medications is at least four weeks
(please see "Treating Saltwater Ich"treatment information elsewhere in these pages), the unfortunate hobbyist is often forced to sacrifice either the invertebrates by moving them to another tank (if one is available) or the fish by risking ineffective treatment. To further complicate matters, salt water invetebrates are suspected of being "carriers" of "ich", and since a suitable treatment has yet to be utilized,
suppliers cannot guarantee that invertebrates are free of these parasites.
The novice saltwater hobbyist is advised to weigh the risks of the mixed collection against the obvious benefits and to make plans accordingly. Freshwater dips and quarantine tanks can reduce the chances of newly acquired specimens introducing disease to an established aquarium. Low fish population density (few fish in a large tank as in the currently popular "reef" type aquariums) may reduce epidemic outbreaks and allow fish to deal with parasites in their natural manner. It is hoped that new advances
in disease treatment and a better understanding of parasite control will lead to a higher degree of success with mixed collections.
The information in this guide is based on aquarium literature, personal
experience and customer feedback. Exceptions are always possible, but these
guidelines should give a basic understanding of the normal behavior of aquarium specimens. Many factors, including tank size, water quality, available hiding places, and even the order in which specimens are added, can affect compatibility.