Posted on Leave a comment

Acclimating Saltwater Fish

Clownfish in Anemone

Acclimating saltwater fish to your aquarium is sometimes overlooked as a beginner. You get the fish home from the LFS or local fish store. You assume since the fish is saltwater and you have a saltwater tank that all you need to do is add the fish and water to your tank. Most of the time the water chemistry is never the same between two tanks. Fish need proper acclimation for a comfortable welcome to their new home.

What is Acclimation?

Acclimation is the gradual process of introducing a fish from one tank to another. Its all about the water chemistry. Temperature is mostly always lower at a fish store so they can save money on salt. Certain health issues are reduced for fish that are kept in lower salinity or even hyposalinity. The fish store’s temperature may be pretty close to your tank at home but the temperature drops in the bag that the fish is in drastically. You want to slowly acclimate your new fish to your tanks temperature and salinity.

Why you should acclimate?

If you choose to not acclimate your fish, they may appear fine and healthy at first but in the near distant future they may die a sudden death. Issues like organ failure, rapid salinity change or temperatur change can really be detrimental to a fish’s health in the short term and long term. You should acclimate your fish to make sure they receive the best care possible during the transistion from their old home to their new home.

When to acclimate your fish

Aytime you buy a fish and bring it home you need to acclimate it. You may also need to drip acclimate fish if you are moving them out of a quarentine tank or just between tanks. It just depends on how close each tank’s salinity and temperature is. Ideally you want them to be the exact same.

Beware of bad fish tank water

Never add water from one fish tank to another. You really do not know what is in the water. There could be copper, which is used to treat sick fish or prevent fish from becoming sick. If you happen to add water that has copper in it to your fish tank your corals, invertabrates or other fish could die if the levels are too high. There could also be microscopic pests or pest eggs that can haunt your tank months down the road and you will never realize how they got in there. You want to play it safe and never add a single drop of water from any fish tank to your tank.

The cup method vs The drip method

The cup method

There are two main methods in which you can acclimate your fish. The first one being the cup method involves adding the bag the fish is in to your tank to let the water heat up to match your tanks water. You then open the bag and use a clamp to attach it to your tank. Take half of the water out of the bag and dispose of it, making sure not to let one drop get in your tank. Then, take a cup of your tank water and slowly pour a little bit of it into the bag with the fish at a time.

Add about the equivelent of 2 shot glasses every 5 minutes. Once the bag is to its original volume, discard of half of the water and repeat the process over again until the temperature and salinity in the bag match your tank. This could take several hours so you will need tp practice patience and take your time. If you are impatient or just do not have the time, the drip method may be more suitable for you.

The drip method.

The drip method involves additional items and additional setup than just a cup and a clamp. You will need a smalll bucket such as these 2 1/2 quart paint mixing buckets from Home Depot of Lowes, a small heater, aquarium airline tubing, adjustable airline valves, two clamps and a cup.

Put the fish and the water from the bag in the bucket below the water level of your aquarium. Add the heater and make sure its plugged in. The heater I linked to above works very well for temperature acclimating small amounts of water. Take out as much water as you can from the bucket and discard of it. Make sure to leave enough that the fish can still swim normally and keeping the heater fully submerged as well.

Cut a piece of aquarium airline tubing. This will go from your tank to the bucket. Add the adjustable airline valve to one end and put the other end in your aquarium so you can start a siphon. Clamp the airline tubing to your tank so it does not fall out, create a siphon on the other end of the tube by sucking on it. Once water goes over the edge of your aquarium, quickly put the other end of the tubing with the adjustable valve on the inside side of your bucket. Use a clamp to keep it in place.

Now you can adjust the flow coming from your aquarium to be about a drip or two a second. The longer you the fish drip acclimate the better it will be. Check on the bucket periodically to make sure it has not overflowed. You may also have to use your cup to pull out water, lowering it in the bucket so more water from your aquarium can drop in. Once the bucket’s temperature and salinity match the aquarium the fish is going into, you can take the fish out and put it into your aquarium. Remember do not add any water from the bucket to your aquarium.

pajama cardinalfish

Ammonia Spikes

When you order fish online, ammonia builds up in the water during transit due to the fish using the bathroom in the bag. Once your fish arrive you open the bag and the fresh air mixes with the water and the ammonia quickly becomes toxic to the fish. You cant drip acclimate these fish, you cant use the cup method to acclimate them. What do you do?

Prior to ordering the fish you need to find out what salinity the fish will be in from the vendor. Hopefully your tank matches perfectly. If not you need to setup a temporary holding tank or bucket that matches the vendors salinity level. Also make sure this temporary tank or bucket is heater to match your main aquarium. Once the fish arrives flot the bag in the temp tank or bucket for 20 minutes. Open the bag and immediately check the salinity of the water. If it matches, take the fish out and put it directly in the holding tank. Let the fish settle for an hour to get his bearing straight. Then you can add it directly to your main tank.

If the salinity in the bag does not match what the vendor tells you then you will need to quickly adjust the salinity of the holding tank so it matches. You can lower the salinity by adding rodi water to the holding tank or raise the salinity by adding premixed saltwater to the holding tank. Most of the time fish purchased online will come in lower salinity water. Once the bag water and the holding tank salinity matches, add the fish in the temp tank/bucket. Let it rest for an hour, then add it to your main aquarium.

If you fail to do the above to fish purchased online or fish that have been in a bag several hours your fish could die very soon up to a few days. Ammonia causes a fish gills to burn and not be able to breath oxygen. Ammonia also causes organ damage to your fish. Your fish may die a few days later due to this and you will wonder why it died suddenly.

Monitor your fish

Closely monitor your new fish for the next several days to ensure it is swimming correctly, doesent have any signs of stress or illness and is eating. It is normal for a fish to not eat a day or two after you get it. Its most likely scared and trying to find a safe spot to hide from the other fish in your tank for safety reasons. Once it gets adjusted and feels safe again it will come out to eat.


Drip acclimating a fish can be time consuming but its very easy compared to other things we do in the hobby that do not involve a life. Once you learn the simple ins and outs of acclimating fish its not very hard or time consuming at all and becomes second nature. Take the time so you can enjoy your fish and see them swimming happily in your tank for many years to come. Your fish will thank you!