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Discussion Starter · #1 ·
I've been doing research. Lots of it. And I've come up with a simple way of guiding some of the new (and the older) aquarists with their stocking.

Before I begin I would like to say:

Each fish is different. Do not assume that they all conform to the below ideas. (I know I wouldn't)


  • Length: 4x the fish's length from head to tail fin.
  • Width: 1.5x the fish's length from head to tail fin.
  • Height: 5x the fish's height from the top fin to stomach.
(Length = longest side. Width = shortest side. Height = top to bottom)

The fish need room to swim in one direction and to turn without bending. They need height to feel safe in the water and to be given a preferred swimming position. The size of your largest fish determines the size of your tank.

No, it doesn't. Some fish need a tank 6x longer than they are due to activity level. But, it's the minimum for all fish. No matter what, don't go under it. By all means, go above and beyond.

Most of us have heard this one somewhere along our journey. Most of us believe it, until we realize one simple fact:
How could a 12 inch goldfish fit in a 12 gallon tank?

The issue with the rule alone is that it is missing the above tank size rule. Once that rule is met, the inch per gallon rule becomes more applicable.

But, still, 12 gallons of water isn't enough for a 12 inch goldfish regardless of the dimensions of the tank. Imagine have 6 twelve inch goldfish in a 75 gallon. Seems a little much, right?


Most fish are exceptions to the rule. Which, is fine really. It's only meant to be a guide. My goldfish example above is one of my favorites, and one I've spent the most time thinking about.

Here are a few exceptions I have found:

  • Goldfish (waste makers)
  • Schooling fish (species only)
  • Aggressive fish (6 male bettas in a 20g anyone?)
  • Young fish (more accepting)
  • Calm fish that don't move much
  • Very active fish
  • Fin nipping fish

This is where I'm going to ask for everyone's help. Let's make a list of fish and how many gallons they would need in a community tank and per other species of fish.


  • Species name: Gallons in a community tank
    • Gallons in a species-only tank

  • Goldfish: avoid other species
    • 2 gallons per inch
  • Guppies: 1.5 gallons per fish
    • 1 gallon per fish
  • Platies: 2 gallons per fish
    • 1.5 gallons per fish
  • Mollies: 4 gallons per fish
    • 3 gallons per fish
  • Serpae tetra: 2 gallons per fish
    • 1.5 gallons per fish
  • Male betta: 10 gallons per fish*
    • 50 gallons per fish*
* = may vary depending on the fish!

That's all I'm going to do for now.

Please, comment. Add to this list. Dispute anything I have said if you have found something to be different. I will add your dispute to the above as I see them.

It would be helpful if you have any issues with the above or would like to dispute something that you put it in red.

It would be helpful if you have anything to add to the list if you would put it in blue.

I will give each member credit when you add to the list. If anyone has any issues, they will know just who to contact.

Let's make a list to help everyone out!
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