How to Add New Fish to Your Saltwater Aquarium – 5 Most Common Mistakes and What to Do About It

Nothing is more fun to the owner of a saltwater aquarium than picking out a new fish (or several) for their saltwater aquarium and then getting it home to add it to their tank. It is so fun and exciting and is probably one of the most enjoyable aspects of the saltwater aquarium hobby. But unfortunately, nothing is more frustrating than going through the whole process of getting that new fish home and adding to the tank, only to have it die within a week, or worse, a disease outbreak occurs and all your fish get sick. The good news, is that most of the time, these losses are avoidable. And I am about to show you how

Mistake #1 – Adding one fish at a time – When adding new fish to your saltwater aquarium, it is often problematic to add just one fish at a time. The reason for this is that the new fish is ganged up on by the resident fish, which is often too much aggression for the new fish to handle. And if you are adding just one fish, then all that aggression is focused on one fish. Sometimes it is the new fish that is being aggressive, but not usually. Another problem with only adding one fish at a time, particularly to a new tank, is that there are not that many fish in the tank, so they take much longer to learn acclimate to their new diet of flakes, pellets, frozen foods, etc.. When you only have a couple of fish in a new tank, they are often stressed out and anxious because they do not have the safety in numbers benefit of being in a school.

Solution: Try to avoid adding just one fish at a time. Instead, add new fish in groups. Make sure you do not go overboard with too many fish, but they will definitely do better when added in groups. Social feeding response improves the speed at which new fish get used to eating the foods you offer. And, by adding fish in groups it dilutes any aggression from resident fish (dilutes aggression); often adding just one or two fish can result in the resident fish picking on them and stressing them out and even injuring or killing them

Mistake #2 – Not acclimating new fish properly, or not acclimating them at all – I am often surprised at how many different and wrong ways I have heard on how fish are added to a tank. Some people get home from the store with a new fish and in they go. Others will float the fish in the bag, in the tank, to match temperature, but do nothing to match salinity or pH. Depending on where your new fish is coming from, the acclimation method used may vary slightly, but the same basics will always apply.

Solution: Follow a proven and thorough acclimation method

turn off lights (make room dark); this minimizes stress on the fish being acclimated and it also lessens the likelihood of aggression from resident fish
prepare the acclimation bucket with tank water that has then been adjusted to match the temperature, salinity and pH of the water in the bag (that the fish was transported in) – and then put the fish into the acclimation bucket
use an air stone in the acclimation bucket or container to keep oxygen level up
using flexible airline tubing, start a siphon from the tank to the acclimation bucket, and continue until pH, temperature and salinity in the acclimation bucket match that of the display aquarium
Mistake #3 – Using a net to move the fish – Whenever possible avoid using a net to move the fish. And if you do need to use a net, then use one with the finest mesh possible, so that it minimizes abrasion and harm to the fish. Do not get me wrong – sometimes you just have to use a net to catch a fish out of a tank. But when it comes time to move the fish from the bag into the acclimation bucket or from the acclimation bucket into the tank, there really is no need for a net.


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