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You are here: myPetSmart.com > Pet Care Library > Ask An Expert > Answered Questions > I Recently Purchased A 36 Gallon Aquarium As An Upgrade For

I recently purchased a 36 gallon aquarium as an upgrade for my 2 fantail goldfis...


I recently purchased a 36 gallon aquarium as an upgrade for my 2 fantail goldfish that were in a 10 gallon tank. I let the tank run empty for about 48 hours before putting my 2 goldfish in. Before they always were swimming around and were good eaters. Now all they do is hide behind a plant decoration and hardly ever swim around and hardly eat at all. At first I thought they were in shock, but after 5 days I don't know what to think. I checked ammonia, nitrate, and nitrite levels and all were good. One of my fish did develop a fungus on one side of his body, and I am treating him with Primafix. What could be wrong with my fish?

In new aquariums, there aren't any beneficial bacteria to break down the fish waste into nontoxic components. It normally takes about 4-6 weeks to develop adequate biofilter bacteria activity. This lack of bacterial breakdown of wastes can result in "New Tank Syndrome," and is harmful to your fish. You may need to do weekly (or more often) partial water changes to keep the tank healthy. Be sure to use water dechlorinator when doing water changes. You can also add some bacterial supplements which will speed the process of populating the beneficial bacteria in your biofilter.

PetSmart offers free water quality testing, and I would recommend you double check your aquarium water quality frequently. Ask a PetSmart associate for free care guides on setting up an aquarium and on water quality for more information about "New Tank Syndrome." Once your aquarium is balanced with adequate beneficial bacteria, your goldfish will be happy to be in their larger home.


23 Jan 2011 3:36 pm

BeavisMom62 said:

When you added your fish to the new tank, as mentioned above, there were no beneficial bacteria in your tank. Running the tank for 48 hours is good, but does nothing to cycle the tank. The "fungus" could be due to stress of living in an uncycled tank. Please make sure to do water tests at least daily for a few weeks and when you see the ammonia (and then nitrite and then nitrate) start to rise do a partial water change. Even if there is no change in these levels, you still need to do at least a 50% weekly water change. Goldies are messy fish with lots of waste, which not only contributes to the ammonia in the tank, but they also give off hormones and other things which you can't test for. They always need fresh clean water.

Primafix is not really a medication but rather a natural remedy. Personally, I would recommend Jungle's Fungus Clear. I've used it twice on my goldies with complete success. There are other fungal/bacterial remedies as well. Another good one is Kanaplex, as it is a broad-spectrum antibiotic. Lots of times, unless the fish had an obvious injury, what you think is a fungus is actually a bacterial infection, for which antibiotics are needed. Just be sure you know what you are treating for. Overuse of antibiotics can eventually create bacteria which are "immune", so use judiciously.

By the way, great job in upgrading to a larger tank for your goldies. That is my biggest pet peeve - that most people keep goldies in tanks (or HORRORS! Bowls!) which are too small for them. As you must already know, goldies need preferably 20 gal for the first fish and 10 gal for each additional fish. Your tank is a WONDERFUL size!

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