Determining the Right Size Tank - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 7 Old 01-28-2012, 05:24 PM Thread Starter
Determining the Right Size Tank

Hey Everyone! I am doing some research on fish keeping and the proper equipment and was wondering how you determine the right size tank to get for specific fish?

For example: If one wanted to set up a freshwater community tank with fish that range in size from 2.5 to 3 inches in length (fully grown) and the recommended minimum tank suggestion for all those fish species is 24 to 30 inches in length, can you look at tanks 30 inches in length, or is there a different calculation one has to use because there will be multiple fish in said tank, and the actual length of the tank has to be longer?

Thank you for your help.
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post #2 of 7 Old 01-28-2012, 07:20 PM
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You also need to take into account the aggression level of the fish.

Also the size of the tank is NOT going to be it's said size once you add substrate, decorations etc, these will reduce the overall volume of the tank.

Smaller tank sizes also mean less room for breakdown of toxins. It means you have to perform more maintenance. The larger the tank size the more time the toxins have to breakdown.
The waste that the fish produces also needs to be taken into account. A larger fish producing a lot of waste in a small tank again will lead to problems and hence a larger tank might be better.

Truth is the one inch of fish per gallon is not very accurate anymore.

10g Fry / Hospital / QT tank (as needed)

75g Saltwater Reef, Ocellaris Clownfish, Lyretail Antias (baby), Lemon damsel, Longtail Fairy Wrasse, purple dottyback, snails, crabs and a few LPS corals.

220g Still sitting empty (come on Lottery I need the numbers to come up!)
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post #3 of 7 Old 01-28-2012, 11:16 PM
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55 gallon or 40 gal breeder tank would be my choice with the 40 gal being number one.

The most important medication in your fish medicine cabinet is.. Clean water.
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post #4 of 7 Old 01-29-2012, 05:59 AM
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2.5 to 3 inches are your fairly average small fish. Community fish, generally, are schooling fish which means you need at a minimum 6 of each species.

So for example with two species, that's 12 fish. The "1 inch per gallon" rule is a very general ball park, but it can get you an idea of what you'll need. So using it, you get 30 - 36 inches of fish, so you would probably want a 40 gallon tank.

For length of the tank, just take the largest number and use that as the minimum you'll need. Tanks come in various widths and heights that make it less than intuitive on their capacity if you only look at length. For example both a 55g and a 120g tank are both 4 feet long (48 inches).

At the top of the pages here on the blue bar is a link for Tropical Fish Profiles, read over the fish you'd like to make sure they get together well, and see if they are schooling or not.
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post #5 of 7 Old 01-31-2012, 12:43 PM Thread Starter
So a minimum of 40 gallons for about 6 peppered/spotfin cories and 6 black widow/skirt tetras? Or would a 20 long tank be adequate?
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post #6 of 7 Old 01-31-2012, 12:53 PM
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I have 6 Serpea Tetras and 4 corys in a 20g (tall) with live plants and would consider it fully stocked. The Black Widow Tetras are larger than Serpae Tetras. I'd do a 29 gallon if you can (or of course larger).
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post #7 of 7 Old 01-31-2012, 07:42 PM
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This is one of those situations where length is more important than volume, given the named species. The 20 Long and the 29g are both 30 inches in length. Either tank would adequately serve for a shoal of the named tetra and corys. I would myself go with the 29g (the "footprint" of both is identical) assuming you have the height [where the tank is going to be placed]. This allows a bit more opportunity for aquascaping, and gives you a bit more water volume which helps "cover things" as someone pointed out. But I would not add more fish in the 29g, since the physical area is the same in either, and for both these fish, that is critical. Live plants also improves things, along with regular water changes.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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