With an established marine aquarium, disease prevention is a mandatory task. The typical method to prevent the introduction of diseases is to quarantine new livestock for 4 weeks in a dedicated quarantine tank. This is a tank set aside for this purpose and typically is set up without invertebrates so that medication may be administered if necessary.

However not everyone has the resources to maintain a quarantine tank, and some livestock is too large for any but the most extreme sized quarantines. Additionally you may have issues with your livestock within the display tank picking up a disease or parasite. This is due to a weakened immune system cause by environmental factors.

The puffer shown below has picked up an ich infection due to ammonia poisoning. Note the white cysts on his skin and fins. Puffers are especially susceptible as they have no scales. This also means that most copper based ich medications can be fatal to them.

For these issues the solution is to do a freshwater dip. Fish can osmo-regulate much more effectively than invertebrates can. This means a marine fish can withstand freshwater conditions far longer than most parasites can without long term damage or even ill effects. The freshwater dip is so efficacious that it is standard procedure for most of the larger marine importers.

Material needed

Baking soda (calcium carbonate)

High range pH test kit

RO/DI water

Air pump, tubing and airstone

Container for the dip (tupperware is my preference)

Methylene Blue (optional)

Large container containing mixed saltwater from the display (optional)

I first will aerate the RO/DI water for at least 3 hours using the air pump and an airstone. This will help stabilize the pH of the water.

I then float the RO/DI water in the display tank to equalize the temperature, this could also be accomplished using a heater, but may melt the container if care is not taken.

I’ll take a sample of the display tank and measure the pH of the salt water in the tank. I’ll use this sample to match the pH of the RO/DI mixture against.

Once the temperature is equalized I will then slowly mix in baking soda one tablespoon at a time to match the pH of the display tank. I let the RO/DI mix sit for 15 minutes between measurements.

It is important to match the pH as closely as possible. This experience will be stressful on the livestock regardless, but it is best to minimize the difference in water conditions. Once the pH is as closely matched as possible you can then add the Methylene Blue (optional).

Once the pH is matched I’ll then net the fish and place it in the RO/DI mixture. I’ll closely observe the fish to ensure it isn’t too distressed. Leave the fish in the RO/DI mixture no longer than 5 minutes! Once the fish starts trying to leap from the container, starts thrashing or breathing very heavily (more than 80 breaths a minute) remove it from the RO/DI mixture and either return it to the display, or if you used the Methylene Blue place it in the rinse container. If the fish is added to the rinse container, let it sit in that container for 2-5 minutes to fully rinse the Methylene Blue traces from the fish.

As you can see with the images below it can be a stressful experience for the fish! It also can be a lifesaving measure however, so it definitively beats the alternative!