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Acclimation Methods


Crazy Crab Lady
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Global Moderator
Jul 23, 2004
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Hello everyone. We're missing a lot of general info sorts of posts around here, so here is one to try to fill it in for at least one area: acclimation methods. What I have written here is based on a combination of direct experience with a lot of different invertebrates (and some fish) and discussions with many other hobbyists on the topic. Please feel free to discuss the subject here, but at the same time, please do not simply give one-liner examples like "I acclimated my shrimp in half an hour and it was fine." Concrete examples are great and can help other hobbyists a lot, but details are incredibly important. Case examples will only be useful for this topic when they include measurements from the bag and tank (specific gravity at a minimum) and also information on how long the animal has been in the tank. Reasons for this are explained below.


Acclimation Methods

It is quite common for people to either drip acclimate or acclimate with more rapid water transfers for a fixed period of time, such as 1 hour, 2 hours, etc. While this works for many animals in many tanks, it is actually a rather risky practice when an important step is neglected: determining how different the bag water is from the tank water. Obviously an animal does not need to be acclimated at all when moving between identical water, such as from a display tank to a sump connected to the same tank. When the bag/tank water difference is extreme, such as bag water with a specific gravity of 1.018 and pH of 7.5, and a reef tank running at 1.025 and 8.4 respectively, even a seemingly lengthy drip acclimation can easily kill some animals. Deaths from rushed acclimation are often not immediate, and some invertebrates will slowly decline over up to a week from such an event. Testing specific gravity is sufficient for most organisms to plan and monitor an acclimation, but testing pH as well is worthwhile with more sensitive animals. When the pH is quite different, testing other parameters like KH may be worthwhile too (mainly in extreme cases involving very sensitive animals like Echinoderms).

Drip acclimation: a length of airline tubing siphons water from the display tank with the rate regulated by a valve (a regular airline valve works). The bag containing the animal is often drained to half or a quarter full and then filled one or more times until the differences between the tank and bag water are negligible (in other words, not detectable on test kits). The bag is often then floated in the tank to allow the temperatures to equalize before adding the animals to the tank.

Drip acclimation is the safest way to acclimate any invertebrate, even hardy ones from tidal areas. If the tank and bag water are only off by a small amount, such as no more than 0.002 for specific gravity and 0.4 for pH, then most invertebrates can be successfully acclimated within 1-2 hours this way with drops at a rate of 1/sec initially and 2/sec or slightly faster towards the very end of the acclimation. If the bag and tank water are very different such as the extreme case presented farther up the page (e.g. bag water of 1.018sg), then go slowly at a drip rate of 1/sec and test the parameter that was farthest off every hour to monitor the progress. When it looks to have equalized with the tank, test the other parameter(s) to verify that you are done.

Echinoderms require extra care. This group includes sea urchins, sea stars, brittle/serpent stars, and sea cucumbers. Echinoderms have demonstrated extreme sensitivity to changes in water parameters in the aquarium and must be acclimated with increased caution as a result. When the water difference is small, such as no more than 0.002 for specific gravity and 0.4 for pH, echinoderms are generally acclimated much more slowly over period closer to 4 hours. This means starting with a larger volume of water in the bag and dripping at a slower rate. Safe acclimation of an Echinoderm can take much longer when the bag and tank water are drastically different. Unfortunately, Echinoderms do not show signs of immediate stress when acclimated too fast, so there is no warning that it is being rushed until it is too late. For example, even relatively hardy Echinoderms like brittle stars will lose arms in the following few days, sea urchins will start to show spine loss within a day or two, and true stars will literally start to fall apart slowly. Because of this risk and delayed result, many hobbyists will still do 4 hour drip acclimation even when the bag and tank water are known to be very similar.

Adding tank water to the bag every 15min: this method doesn't really have a name, but generally involves draining the bag to a quarter full and then filling it by a quarter more with tank water ever 15min. There are many variations on this method adding water at different rates, sometimes only draining the bag to a half and then filling it more than once, etc. The main feature of this approach is that it adds reasonably large volumes of new water to the bag in rapid bursts, rather than gradually as in drip acclimation. Many fish can handle fairly rapid changes in salinity without much stress, so this method is often used as a means to minimize the time that fish spend in dirty bag water, where it is argued that the stress from prolonged exposure to waste in the water can be greater than the stress from a small, rapid change in other parameters. While some invertebrates can tolerate this kind of acclimation, it is unwise particularly when the bag water hasn't been tested and when the hobbyist is unfamiliar with the native range and habitat of the animal in question. Fish foul the bag water far more than the average invertebrate, so the same waste-related motivation does not exist for invertebrates.

Temperature-only acclimation (NOT RECOMMENDED): the bag is floated in the tank to equalize the temperatures and then the organism is placed directly in the tank. This practice should be avoided even though it is alarmingly common in some parts of the marine hobby. The only exception would be if you removed an animal from a tank, allowed the water removed to become cold, and then need to re-add the animal to the same tank. If the waters are different, temperature-only acclimation accomplishes very little in the way of alleviating stress on the animal. Fish can often survive the method, but invertebrates are more likely to be killed in short order. For every hobbyist who claims to have total success using this method to acclimate marine animals, there are too many others who come to forums asking for help on why their animals keep dying within a couple of days of this sort of treatment. The difference is likely accounted for by the success cases being lucky instances where hobbyists have been able to keep their tanks' water as close as possible to the water at their local stores - something that is not always possible or a good idea, particularly for stores that keep their tanks at very low specific gravities to fend off fish diseases.