Goldfish: Tall or Long tank?

Question
Hi Nicole, you've helped me tremendously with another question in the past, so I wanted your opinion on another slight quandry of mine.

I'm expanding my fish-keeping operation and would like to put my two juvenile goldfish into a bigger tank as I know goldfish should have at least 10 gallons of water each. However, I have two choices of tank shapes: tall (approx. 24" long, 20" high) or long (approx. 30" long, 16" high).

The long tank has greater surface area per gallon, which means more oxygenated water (I rely on gas exchange via the water surface agitation from an HOB filter.) The tall tank, however, has more vertical swimming room, which I hear goldfishes enjoy since they are the kind of fish that like to swim at all levels.

So what do you think? Does the tank shape matter in keeping happy goldfish, or is it merely a stylistic preference? Thanks for your advice in advance. :)

Answer
Hi Roger,

I would definitely suggest you choose the long tank over the tall tank. While goldfish do enjoy swimming at all levels, the increased surface area (which means better gaseous exchange) is going to be the most beneficial to goldfish, who thrive in highly oxygenated water. That's another reason they do better in cooler water, because the warmer the water, the less oxygen it holds. Ideal temps for goldfish are in the high 60s to low 70s, but they are very adaptable.

The "best of both worlds" would be to get a 29 gallon tank instead of the 20 gallon long tank - it's what I keep my two black moors in. The dimensions are 30.25" x 12.5" x 18.75". I can tell you that they do use the height of the tank somewhat, but they mostly inhabit the middle to bottom levels. A 29 gallon tank is a very standard size here in the U.S. (not sure about Canada or abroad).

One bit of advice that I have for you is to make sure to offer plenty of filtration. If you are taking the HOB filter from a smaller tank, it may not be powerful enough to filter a bigger tank. Goldfish produce lots of ammonia for their size, so they need powerful filtration. I would recommend 8-10x turnover, so if you have a 20 gallon tank that would mean 160-200 gallons per hour (gph). Look at the flow rate of every filter you buy to determine the gph.

In my 29 gallon goldfish tank I have an undergravel, an additional airstone, a Magnum HOB filter, and an additional 100 gph HOB filter. Between the two filters, that's 350 gph, then there is the additional water circulation provided by the airstones. The goldfish seem to appreciate every bit of this water movement and oxygenation!

Take care,
Nicole