Just as it is important to match fish with similar dispositions it is also important to acclimate fish properly. Acclimation is the process of gradually introducing a fish to its new surroundings and tank mates. It is much more than simply dripping the tank’s water into the bag over fifteen minutes.  A new fish has to overcome three things when introduced into a new tank:

1. The fish is usually stressed from capture and shipping before being placed in its permanent new home.
2. It has to acclimate to its new home and food.
3. Lastly it needs to fend off the aggression of the previous residents to the tank. 

     For these reasons the initial two weeks after a fish is purchased is usually the time frame when they are at greatest risk. A newly purchased fish should not be simply dumped into the display tank, but it should be gradually acclimated to its new home in a separate tank to reduce the risk of it introducing a disease. This quarantine period also allows it to become accustomed to feeding in a captive system and also become accustomed to new water conditions. For these reasons one of three general philosophies of acclimating a new fish should be employed:

1. In the best case a quarantine tank should be utilized to acclimate the fish as well as get it accustomed to eating. There are many articles dealing with quarantine tanks so we won't deal with them here. Also, since less than 2% of all fish keepers have quarantine tanks they are not how most people will be able to deal with this problem. In the case of a tank with a sump, the sump can be used as the initial home for the newly acquired fish.  If a sump is available, it should be secured so that the pump intake is screened to make sure that the fish is not drawn into the pump intake and killed.  The fish should be acclimated to the new water per the directions below. The fish should be kept in the sump for approximately two weeks at which time the next phase of acclimation should be conducted.
2. This next phase is what those of you who do not have a sump in place should do.  In this phase a holding container is placed in the tank and the fish is placed in it. For this purpose a large (two gallons in size) clear plastic box is attached to the inside of the tank. Lots of holes are drilled in the bottom and sides of the box so that the tank's water can flow freely into the box.  In addition the output from a powerhead can be directed to flow into the box so that there is constant new water flowing through the box. If a sump is unavailable the fish should follow the initial acclimation process outlined below and then placed in this box. This clear box allows the new fish to view its new surroundings and tank mates and in addition it allows the tank's residents to view their new tank mate.  The clear box will also encourage any fish with aggressive tendencies to show them by charging the fish in the box. At first the fish in the box will cower when approached by the tank's residents. A lot of aggressive displaying will occur as well as mock aggression. However the clear box will prevent any damage from being done and over time (usually two to four days) the frequency and intensity of these attacks will diminish. By seeing which fish continue to attack you can also note where future attacks may come from. The fish should be kept in the box until no attacks occur, this may take from anywhere from 2 to 10 days.  However even after this period of time attacks may continue.  If after this time attacks are still occurring, even if infrequently, a next step needs to be taken.
3. This step entails removing the aggressive individual or individuals and placing them in the box, while at the same time releasing the new individual into the tank.  This step is necessary because the tank's older residents have established territories and know the tank's hiding places and if a new fish is introduced while they are still present the new fish will be at a distinct disadvantage which usually results in the new fish either getting killed outright or being harassed to such an extent that it never eats and eventually dies.

     There are several things that can be done to reduce this aggression once the tank's older residents are re-released back into the tank. The coral or other landscaping materials can be rearranged in order to make the old fish establish a new territory. In addition, if the fish attempts to attack the newcomer even when it has been placed in the box then several new fish should be added to the tank before this older fish is released back into the tank. By adding more than one fish the aggressive tendencies of the older fish will be more spread out and thus each fish should be able to tolerate it.  More than one fish needs to be introduced whenever you are adding a fish to a tank that already has a member of that same species, as fish are generally most aggressive when confronted with new members of their own species particularly damselfish, tangs and dwarf angelfish. In addition, they are also aggressive to members of their own genus as well as fish that are physically similar in terms of coloration or physical shape or fish, which have a similar diet.

     As mentioned above once you have set up a tank properly most fish are hardy and will do fine. Proper acclimation is as crucial as proper selection, as doing both properly will help to avoid problems with aggression, disease and nutrition.

            Having discussed general philosophies, we now move on to the actual acclimation procedures. The following procedures are recommended to safely and successfully introduce your newly arrived aquatic animals to your holding systems. More animals are lost due to poor or insufficient acclimation procedures than virtually any other factor. Moreover, it is not uncommon for animals to die days or even weeks after arrival specifically because they were stressed and/or damaged during acclimation.

            During shipping your new fish or invertebrate is confined inside a plastic bag without any of the normal filtration and temperature control it has been used to. Even though we ship using the latest and most advanced stress coats, ammonia reducers, and pH buffers, because the animals are alive all of their metabolic processes continue inside the bag without any way for their natural waste and respiratory products to be completely removed. Additionally, even packed in insulated containers with temperature packs, during shipping the animals can be exposed to greater temperature fluctuations than normal. The net result of all of this is a decrease in pH, a rise in ammonia, and often enough a temperature shock. All of these have a cumulative effect to put your animal into some degree of stress and even shock after transit.

            On top of all of this, we hold all fish in hyposaline conditions (specific gravity of 1.018) to inhibit the proliferation and transmission of a variety of ubiquitous parasites and pathogens. If your system water is not hyposaline, the transition from hypo to relatively hyper saline water can be extremely stressful, if not fatal, when handled improperly.

            “Acclimation” is simply a way to introduce the animals safely from the relatively toxic conditions of their shipping bags to the healthy and safe conditions of their new home. Even though you may think that it is important to get your animals out of the bag and into your clean holding systems as soon as possible, it is extremely important to remember that too rapid a change in water conditions can be far more dangerous to aquatic animals than being kept longer in a relatively bad environment. It is this slow transition from one aquatic environment to another that is the focus of our acclimation procedures. REMEMBER – SLOW IS GOOD, so take your time!

            We take great pride in holding our animals under exceptional care and husbandry regimes. Having said that, please note that we recommend that all newly introduced animals be quarantined first to prevent the introduction of any potential disease and/or parasites to your aquarium systems. If you do not have a quarantine system available (and even if you do) it is important that a commercial “fish dip” be used prior to introducing new fish species into your holding systems. DO NOT use any “fish dip” on corals, clams, or invertebrates.

            Very careful attention must be paid to the placement of corals in the reef tank visa vis coral compatibility. Many corals are extremely aggressive hunter/feeders and can inflict severe damage on non-compatible tank mates if not properly separated from them.

Depending on the species and particular circumstances, corals may employ one or more of the following aggressive mechanisms:

• Rapidly overgrowing neighboring invertebrates—i.e., actually growing directly onto the neighboring colony or extending over it and preventing it from receiving life-sustaining light
• Stinging neighbors with nematocyst-laden tentacles
• Extruding digestive organs (called mesenterial filaments) and essentially digesting the tissues of adjacent corals
• Exuding toxic chemicals (e.g., terpenoids) into the water to kill neighboring corals or impede their growth

What can you do to counteract these hostile tactics?

• Research your corals thoroughly before you buy them - A little modestresearch on the characteristics of different corals will reveal all kinds of vital information regarding their relative aggressiveness/noxiousness. For example, Sarcophyton leather corals are notoriously toxic and various Euphyllia corals are known to produce long, stinging “sweeper” tentacles. Such details must be taken into account when choosing which species to combine and how to situate them in your tank.
• Space your corals out properly - When placing specimens, allow more room between them than you think they’ll eventually need. If the tank looks sparse initially, that’s okay. It’s better to have a smaller number of specimens with plenty of room to stay clear of each other’s tentacles than to have a larger number growing on top of one another and in a state of constant warfare.
• Isolate rapid-spreading corals - Corals/polyps that form encrusting mats and grow rapidly outward onto adjacent substrates, such as green star polyps and certain zoanthids, may need to be isolated to a single, separate rock—an island, if you will—to keep their growth in check and prevent them from irritating or overgrowing cnidarian neighbors.
• Maximize water movement - Brisk, turbulent water movement, which is beneficial in many reef-aquarium settings anyway, will help prevent toxic chemical compounds from concentrating around any particular specimen. Keep in mind, however, that not all sessile invertebrates appreciate a high level of current. Some, such as Discosoma mushroom polyps prefer very low levels of water movement.
• Employ a protein skimmer, chemical filtrants, and copious water changes - Vigorous protein skimmingand chemical filtration with activated carbon will help remove/adsorb the byproducts of coral chemical warfare. And, of course, you can add the removal/dilution of these toxins to the many virtues of regular partial water changes.

            The rule of thumb here is that if your coral has tentacles, chances are it is one of these aggressive species (including, but not limited to Catalaphyllia sp., Galaxea sp., Euphyllia sp., Goniopora sp., Heliofungia sp. Fungia, sp, etc.), however, many “fleshy” LPS corals like Trachyphyllia sp. and Lobophyllia sp. can also extend feeding tentacles and sting their neighbors. Anemones are also obviously aggressive “stingers” and should be placed sufficiently far from corals so that their tentacles cannot inflict damage.

            Although mushrooms and polyps are relatively harmless, there are some species that can be semi-aggressive to their neighbors. Same thing applies to “softies”, some of which can secrete toxic chemical compounds from their tissues.

Take a good amount of time to research the species you want in your aquarium to see how aggressive they are! Separate all aggressive species sufficiently from their neighbors. It won’t be difficult to see if they are far enough away because if they are not you will soon notice necrotic (dead) spots on the “victims” in the areas closest to the “stingers”. Also, make sure to re-evaluate the separation as your corals grow and encroach upon each other.

            A little precaution and some constant attention will yield invaluable results and allow you to maintain and enjoy a successful reef aquarium for years to come.