Fish per gallon question (tetras and gouramis) - The Planted Tank Forum
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post #1 of 9 (permalink) Old 06-14-2010, 07:12 PM Thread Starter
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Fish per gallon question (tetras and gouramis)

This question stems from my earlier post, but this one is rather specific. In general, how many tetras can be kept per a gallon? Also, how many gouramis can be kept per a gallon?

If they are being kept in the same tank, do the fish numbers per gallon change? I am considering an ADA 17 gallon aquarium at the moment.
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post #2 of 9 (permalink) Old 06-14-2010, 10:35 PM
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Unfortunately, the "fish per gallon" rule does not really work, as the amount of waste a fish produces is more indicative of how heavily you can stock an aquarium.

For example, ten 1-inch Neon Tetras would be considered "10 inches" of fish. However, a single 10 inch Oscar would produce much more waste than the equivalent "10 inches of Neon Tetras".

In addition, there are various species of Tetras, some more larger bodied than others, meaning they would produce more waste than more slender tetras.


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post #3 of 9 (permalink) Old 06-15-2010, 02:57 PM
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The smallest fish can be stocked more densely than larger fish, even when the difference in size is not as extreme as the mistaken example above. A fish that is twice as long as another fish is also twice as tall and twice as wide. It has 8 times the oxygen demand, and produces 8 times the waste, so needs more water to keep the oxygen available, and dilute the waste. A fish that only grows to 1" produces a lot less waste than a similar shaped fish that grows to 2".

The 1" per gallon guideline works pretty well when the fish are 2" and under. It was never meant to answer stocking questions for larger fish. Comparing 10 Neon Tetras to one Oscar is not using the 1" per gallon guideline correctly, and then saying the guideline does not work. If I start with a mistaken or misstated concept I can say a whole lot of ideas are false.

The 1" per gallon guide does work to suggest some limit of stocking that will still provide the oxygen the fish need, and enough water to dilute the wastes, as long as the fish are small enough.
It says nothing about the social issues of these fish. You could fit several male Bettas in a small tank, and they would have enough oxygen, and their waste would be diluted, but socially it would not work.
It says nothing about the activity level of the fish. You can put a Zebra Danio (about an inch long) in a gallon of water, but the activity level of this fish makes it not work. These are more examples of applying the guideline incorrectly, then saying the guideline is at fault.

If you are thinking about Ember Tetras and Licorice Gouramis you can physically fit a lot of them in a tank. They are very small fish, very small oxygen demand. Very small waste (ammonia and CO2) production.

If the Tetras and Gouramis you are thinking about are Pacus and Kissing Gouramis, then all bets are off. They would not even fit in the tank.

For a small tank you might think about something like this:
(1) Honey or Dwarf Gourami
(6-12) of some Tetra or Rasbora that only gets 1" or so long. For example up to 12 Embers or Dwarf Rasboras or other really small ones, or 6 Harlequins, Glow Lights, Neons or similar size schooling fish. A small group of Cherry Barbs (1M + 2-3F) could work.
(1-2) Otos or (6) shrimp for algae.

"How many fish fit" is not just about how many bodies you can stuff into a glass box, but how well you can maintain that environment when a problem hits. Under great conditions you can keep a lot of fish in a tank. But what happens when the power goes out? No water circulation, poor light (less photosynthesis), no heat...
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post #4 of 9 (permalink) Old 06-15-2010, 03:35 PM
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Originally Posted by cmf0106 View Post
Also, how many gouramis can be kept per a gallon?

Unless we are speaking of dwarfs and or sparkings then I would only keep one Gourami per tank unless you are attempting to breed. Gouramis are classified as semi aggressive but I have had a couple in my lifetime that have been down right aggressive when they are full grown. My currect Three spot is 6 inches which is pretty big for that species and I cannot put anything in the tank or he will kill it. Except some japanese trapdoors in the tank.
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post #5 of 9 (permalink) Old 06-15-2010, 11:10 PM
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Ultimately you will buy which ever fish and how many you want no matter what we say. For the ADA 60-p cube I would only get 10-15 Neon tetras a few Oto's and maybe some shrimp to go in there and call it a tank.

One thing I can see the guys above me left out was Filtration. The amount of fish you can keep also counts on the type and how big your filter is. No matter how big your aquarium you wont be keeping a lot of fish if your filter is sub-par.
Another thing is how much maintenance you are planing on doing to keep the water clean.
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post #6 of 9 (permalink) Old 06-15-2010, 11:16 PM
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Why the fish per gallon or inch per gallon rule does not work:

30 gallon long tank with standard filtration
30 inch Red Pacu as sole inhabitant

or... 3 10 inch oscars

or 6 5 inch jd;s

or 2 Pike Cichlids(not dwarf)

See where I'm going?
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post #7 of 9 (permalink) Old 06-16-2010, 04:19 AM
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Overstocked, you are applying the 1" per gallon guide to fish that do not qualify to be included. Then saying the guideline is at fault.

Properly stated, the 1" per gallon guide works only for fish that are a maximum of 2". Do not talk about larger fish and then use that as an example of why the guideline does not work. If I put lawn fertilizer in my tank, and everything died I could say that fertilizing the tank is bad.

1" per gallon works to assure the fish have oxygen and there is enough water to dilute their waste between regular water changes. It works well enough for fish that max out at 2" long.
It does not address social issues.
It does not address activity level.
It does not apply to larger fish.
It works reasonably well for the standard tank sizes.

An even better guide is this one, with some odd math.
It also applies only to smaller fish.
It helps to distinguish between tall tanks, standard tanks and breeder tanks.
It is based on the fact that gas exchange happens only at the surface of the water, and relates the fishes' need for oxygen to the amount available in a certain area of water surface.
1) Measure the length of the tank, and the width.
~~here is the trick: Measure one way in inches, and the other in feet.~~ (It does not matter which)
2) Multiply.
3) This is how many inches of small fish you could put in the tank, just from the point of view of oxygen exchange at the surface.

No, I do not want to hear that I can keep 24" of small fish in a cookie tray that is 12" x 2' or any other silly variation.

I also had a Cosby (Color morph of the 3-spot) Gourami that tried to claim all of a 125 gallon tank. Breeding Angels stood up to him, and some Jewel Cichlids. Gouramis and their relatives cannot be stocked several to a tank unless you are alert to such issues and willing to move the fish out of a situation that is not working. Some males are so aggressive they attack all the other fish. Some confine their aggression to other Anabantoids, including females that are not ready to breed. The females are often easier to deal with, and may get along, but even with all females, watch it. Some are pushier than others.
Among the commonly available Gouramis I would rank them this way:

Most aggressive:
3 Spot and all the color variations.
Dwarf including all the color variations.
Paradise Fish.

Less aggressive:
Dwarf Sparkling

Specialty set up, perhaps species only:
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post #8 of 9 (permalink) Old 06-16-2010, 04:22 AM
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Re: Fish per gallon question (tetras and gouramis)

The point is simple: there are sooooooo many exceptions to the rule how can you use it? More importantly using it to help people new to the hobby is even more dangerous. I could spend an hour on the exceptions, but I won't.

Sure, in theory it is great, but as a tool for new hobbyists it is junk.

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post #9 of 9 (permalink) Old 06-16-2010, 04:57 PM
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Originally Posted by cmf0106 View Post
If they are being kept in the same tank, do the fish numbers per gallon change? I am considering an ADA 17 gallon aquarium at the moment.
What species of tetras are you considering?

You could easily keep 10-15x Ruby or Ember tetras in a tank that size (along with a few small scavengers such as a school of dwarf Cories), but if you wanted a larger tetra like a Cardinal I'd drop that down to 5-9x.

There are also some tetras that can be pretty aggressive (Silvertips and Blues come to mind...) and wouldn't be good choices at all...

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