What's rules do you use to determine min. Tank requirements?

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I go by:

Riverine or lake species (different DO requirements).

Known territorial characteristics.

Average adult size.

Activity level (active constant swimmer to sedentary statue mime).

Feeding style.

Overall body flexibility.

Body height.

Swimming speed.

Nesting area size.

I think these considerations are perfect

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I often see people saying that certain size tank requirements are necessary for this fish or that stocking plan. I'm just curious what rules or calculations everyone uses to determine minimum tank requirements. Recently I've read people stating that a standard 48" long 55 gallon tank would not be sufficient to home a 6" mature CA cichlid. So got me thinking how do people arrive at these conclusions.

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Why would anyone want small CA cichlids that require huge room?

Go with huge African riverine cichlids. Oreochromis Aureus (Blue Tilapia) max at nearly 20" and hit 12" + in 9 months from fry. An aggressive tight stocking rate requiring good filtration would be 2 gallons per pound. A extremely conservative (lowest rate you should NOT drop below) is 10 gallons per 1 pound.

Adult 15" - 18" blue tilapia average 5lbs - 6 lbs. (That is one massive fish in the 55G).

What shocked be about your post is the 6" thing. A 6" fish is tiny, or some uber juvenile. I would be shocked for a 6" cichlid weighing > one pound (Closer to 1/2 most likely).

You can keep one 6" CA cichlid in the 55G (maximum) or six - ten 6" blue tilapia in the 55G (minimum)!

I do not suggest any strain of Nile Tilapia as they grow way too quickly and breed at just 8 months old for a 55G tank.
 
Why would anyone want small CA cichlids that require huge room?

Go with huge African riverine cichlids. Oreochromis Aureus (Blue Tilapia) max at nearly 20" and hit 12" + in 9 months from fry. An aggressive tight stocking rate requiring good filtration would be 2 gallons per pound. A extremely conservative (lowest rate you should NOT drop below) is 10 gallons per 1 pound.

Adult 15" - 18" blue tilapia average 5lbs - 6 lbs. (That is one massive fish in the 55G).

What shocked be about your post is the 6" thing. A 6" fish is tiny, or some uber juvenile. I would be shocked for a 6" cichlid weighing > one pound (Closer to 1/2 most likely).

You can keep one 6" CA cichlid in the 55G (maximum) or six - ten 6" blue tilapia in the 55G (minimum)!

I do not suggest any strain of Nile Tilapia as they grow way too quickly and breed at just 8 months old for a 55G tank.

The which fish is better argument is not what this thread is about. I'm also not in the boat that I need to keep one 6 inch fish in a 55 gallon. I was just interested in understanding their logic. Currently I have 3 to 4 fish in each of my tanks around 4 to 5 inches and feel that is good for my fish, and makes me happy. I'm sure I'll want to try many other species in my time though.

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Common sense
 
First, I always start off with the assumption that I will keep all the fish I get. Second, I always assume that I'll have them until a natural death.

I determine the stocking and size based on three general requirements:

1) the fish has to be able to reach full size and approach a normal life span---this is the easiest step. I don't get fish that will out grow my tank nor do I plan to sell them, trade them or euthanize them
2) the fish has to at least exhibit normal swimming and feeding behavior----if I can't get this, I stop and either re-size the tank or change the species
3) the fish might be able to exhibit breeding, shoaling and interpersonal behavior---an amazing plus in my mind, and lately I've considered more desirable. I used to not do this.


To determine (1), I use the largest adult size that I can find it has attained in a tank, calculate the full bioload for all fish, and calculate the nitrate level with a weekly 50% WC using 50% protein food at a daily rate of 1.5% of body weight. If the nitrate PPM stays under 20, I assume I can achieve (1) from a health aspect. (The reason for this assumption is that my model has built in tolerances: a) most fish will not reach the absolute maximum, b) I can do more WC% per week and c) the adult maintenance rate is more like .75% of adult weight. So, lots of slack.)


To determine (2) is more complicated, as species differ a lot in this regard. Some species need wood, some need sand, some need large territories, some are peaceful only if given ample space, some are fast swimmer, some aren't flexible turners, some use the upper water column, some are too passive as eaters, some are nocturnal, etc. This is just a long process of examining a lot of components in a tank. Interior dimensions are certainly a large part, but so are tankmates, lighting, and decor for example. Larger tanks definitely help the chance of (2) occurring for swimming, but feeding takes more thought.


To determine (3) requires more considerations beyond (2). More space allows for more species members and certain decor might allow for breeding. More space also allows for more of one species and shoaling. Specific tank arrangements might allow for owner-pet interpersonal behavior like petting or hand feeding.
 
Go with huge African riverine cichlids. Oreochromis Aureus (Blue Tilapia) max at nearly 20" and hit 12" + in 9 months from fry. An aggressive tight stocking rate requiring good filtration would be 2 gallons per pound. A extremely conservative (lowest rate you should NOT drop below) is 10 gallons per 1 pound.

I'm not following. Are you suggesting 50 pounds of fish in a 100 gallon aquarium?
 
I'm not following. Are you suggesting 50 pounds of fish in a 100 gallon aquarium?

This is not my suggestion, it is a general rule of thumb in the industry.

As an absolute maximum, yes. I stay closer to the minimum however, ie: 10 pounds of Oreochromis Aureus (Erroneously classified as Tilapia) per a 100 gallon.

I don't use Aquariums for aquaponics however (Nowhere near sturdy enough!).

TSC has a sale on the 100 gallon Rubbermaid stock tanks with a 1 1/2" drain for $60. The 300G is $249.

I would HIGHLY advise against using any glass aquarium for this type of stocking and would not do it myself for any reason. I doubt that the glass would survive an 8 month fry to freezer growout of any of the three major Oreochromis genus used in aquaponics.

The Rubbermaid stock tanks are soo much stronger then glass aquariums there couldn't possibly be a comparison. These ridiculously cheap perfect aquaponic containers are designed to be kicked by cattle and horses. They also have the 1 1/2" drain threaded on both the inside and outside that can be used to house a deicer for the livestock to have accessible water supply 365 days a year in any state in the USA!
 
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