Inch Per Gallon

[BillD]

A rule that doesn't apply in the majority of situations is a poor rule. You could easily keep 10 neons in a 10 gallon, without filtration. You can also grow out 50 or 60 male guppies if it is filtered, and the water is changed often enough. The number of fish that can actually be kept in a tank are relative to the amount of work one is willing to do. A tank with a big bioload, needs regular water changes, no matter the type or amount of filtration. The amount of water and how often depends on the individual tank. Clean water is probably the single most important factor in getting good growth rates and healthy fish.

 

[krap101]

even in the saltwater side of it a little... tangs get to be what 6"... but they need a 6' tank cuz they need swimming room... so by the inch rule i could have a yellow tang in a 12 gallon nano right... WRONG

What about finding Nemo?

(Just realized my joke might not have made sense, but they had a tang Bubbles )

 

[HooKooDooKu]

even in the saltwater side of it a little... tangs get to be what 6"... but they need a 6' tank cuz they need swimming room... so by the inch rule i could have a yellow tang in a 12 gallon nano right... WRONG

First of all, the 1" rule is a "rule of thumb", and that seems to be getting overlooked in this discusion. Rules of thumb are inherently NOT good for all situations, just a rough estimate.

Second of all, the 1" rule for salt water isn't the same, it's 1" per 3 gallons. So going by the "rule of thumb", a salt water tank of 18 gallons should be able to handle the bioload of ONE 6" tang.

But then again, this is just a "rule of thiumb" and isn't approprate for special cases like the tang.

 

[darkmule27]

x2 HooKooDooKu

Additionally, in order to find the length, it forces newbs to do at least the smallest bit of research. If the fish is an acception to the general rule, it very often says. When you already have the site up for the size, most people will probably read the rest.

 

[DeeDeeK]

how many lungfish before oxygen levels get too low?

Hah hah. Just kidding about that question!

I go by a few rough assumptions when stocking:

a 1" fish is only around a quarter the volume of a 2" fish and is ridiculously smaller than a 4" fish. You must consider not only length but breadth and depth. All that means a seriously large bulk that needs oxygen to survive.

a three inch molly is my base yardstick and I don't go by gallonage but by surface area of the tank. The greater the surface area, the greater the ratio of aeration to volume there is in the tank. So, I go by 1" of molly to every ten or twelve sq. inches of surface. That might mean four or five Alxelrod's Rasboras or three or four Endler's Livebearers. I assume some sort of water movement that causes the surface water to turn over.

for me the big issue is being humane and creating the kind of environment those fish need to thrive. Neon Tetras don't need lot's of personal space, oscars do. African cichlids often like rocks and sand with few plants. You probably can't fit all the fish a tank will hold without denying the fish their needs (other than oxygen). Look at Wal-mart's fish section and see how many fish won't suffocate - but check out their health! See any ich, upside down guys with fat tummies? Any corpses?

Aquaria that are healthy, humane, and pleasing to the eye is my goal in stocking my tanks.

 

[krap101]

Bad thing about surface area is you don't factor in flow and filtration.

 

[DeeDeeK]

Surface area, flow, and filtration

I didn't know that flow and filtration were a factor in inches per gallon figuring. Could you give me a link to a site with that info? I'm really into filtering and using low-volume filters to create surface turbulence to oxygenate and blow off co2. Perhaps flow and filtration factored into gallons makes a difference?

I thought the surface area and inch/gallons theories as they originated was before filtering was very common.

Anyhow, I use a weak filter, less than 20gph, with its outflow positioned at surface level, where it can cause the most oxygenated water to circulate while at the same time displacing it with some oxygen-poor water that's been through a good biofilter. On the bottom I have very loose-packing large grained river sand (smoothish grains good for corys) about three or four inches deep, heavily planted but with open sand here and there. I use cali blackworms and MTS to aerate it and it all works pretty well. The tank is 9 gallons only, with a heap of teeny-tiny fish like microrasboras, sundadanio, and poecilia wingei plus a few giants - gold tetras at 1.5."

My arrangement works very well for me so I assume good filtration and aeration in my working version of inches/gallon. If my filtration dies, I have to move some fish to a less populated tank or else they're all gasping at the surface by morning. I suspect the plants cause that since it happened at night.

 

[krap101]

The reason surface area won't work because it relies on the concept of aeration. More surface area=more oxygen exchange, but more agitation=more oxygen exchange, so I could stock a 20 high the same as a 20 long. Also you're ignoring the area in which the fish swim. (swimming space) That would mean that 20" of tetras in a 20 long would be the same as 10" of tetras and 10" of corys, but in reality, the height of the tank does play a pretty large role.

 

[Yellow Eye Tang]

You have to consider so many elements when keeping fish. The main goal is to give them comfort in their environment. The 1" per gallon rule is awesome when it comes to taking the best care of the fish whether it is a "true" fact or not. It's just a good rule to help keep the fish in the best environment. I have had tanks that broke the rule with no problem at all but I still try to live by it. I don't believe that you HAVE to do it.... but you just want to make sure the fish you purchase are ok with it. It's the same standard as trying to put an Oscar in with goldfish. Over time that probably wouldn't work out for the goldfish. Just know what the heck your doing so it will work for you and the fish.

 

[mike47517]

at first i did but now that im more experienced i say its crap. everything depends on the fish the filtration the actual size af the tank and the water changes.

 

[DeeDeeK]

The reason surface area won't work because it relies on the concept of aeration. More surface area=more oxygen exchange, but more agitation=more oxygen exchange, so I could stock a 20 high the same as a 20 long. Also you're ignoring the area in which the fish swim. (swimming space) That would mean that 20" of tetras in a 20 long would be the same as 10" of tetras and 10" of corys, but in reality, the height of the tank does play a pretty large role.

I do agree about circulation of the surface, by agitation or upwelling. However one square foot of agitated water has half the area for gas exchange as two square feet of agitated water. Therefore, given the same volume of water, we can overcrowd even more fish into the same tank. Probably not twice as many but more. I think Wal-Mart sets the standard for overcrowded fish in their fish concentration camps, erm, tanks.

I'd also say a 1.5" tetra is not equal to, say, half of a three-inch cory. Considering their volume to body length proportions, I'd say you need more than two 1.5" neon tetras to equal one 3" cory. Of course you could have 10" of pygmy corys and 10" of neon tetras and they'd be pretty close . . .

I say if your fish are happy and healthy and you enjoy the way your aquarium looks, then screw 'em (the rules) and do it the way you figured out. I'd been feeling a bit hidebound and decided to experiment and explore and now I freakin' love my fish tank!

 

[Mystery]

I don't think it is only about bioload. Some fish also have behavioral/movement needs.

 

[spoonman]

I think that whether you believe this rule or not you have to take into consideration the ADULT size of the fish you are considering. An inch of Bala shark doesnt continue to be an inch of Bala shark a year down the road after you've added another 10 inches of fish and hes bigger now. Filtration, fish species choices and tank maintenance are bigger facters than how long they are. IMHO

 

[Mystery]

I agree, everyone should anticipate raising the animal to mature size--and you also may need to factor in breeding with some species.

 

[DeeDeeK]

Gold Tetras, mass to oxygen, bugs, plants, worms, the universe and everything

Thinking of movement needs, I have these gold tetras in my li'l tank and that was a mistake. They seem to be a bit stifled to my eye and I'll guess that their experience is even more stifled. Shoot, time to adopt out six of my favorite fish.

Also, I foolishly put one male endler's in with three female endler's livebearers. I hate euthanizing fish, so now I have three broods of babies to grow out a bit and then adopt out. Sheesh. I've thought about adult sizes and bioload but really was a tad careless with space needs and breeding habits.

The cool thing is that my tank foliage is exploding from all the waste from the 4x to 6x daily feedings for the fry. Oddly, the water is still clear(ish) and nitrogen levels are 0 NH3, 0 NO2, and 5ppm NO3. I think my deep sand bed is helping with all this. So are all the flatworms, snails, shrimp, and other tiny mysterious li'l guys eating up the mulm and crapping out bacteria food.

Aeration is being accomplished by one weak internal filter with its outflow at surface level - no bubbles or anything and nobody is gasping. I guess the plants are taking up the CO2 and preventing toxic levels from occurring.

Now how am I to figure out how many fish is cool? It's all so complicated.

I was thinking of switching to all male endler's, sundadanio axelrodi, bororas maculatus, some ottos and keeping my pigmy corys. Maybe some nana rasboras. All the bugs and worms and plants can stay.

Oh, I meant to mention I've been studying Walstad's book, "Ecology of the Planted Aquarium". It has an excellent section on oxygen use, fish size, and relative metabolism. As fish weight increases, metabolism decreases-but not at the same pace is weight increase. So, more smaller fish DO indeed use less oxygen in general, per inch, than bigger fish. That is because the fish weight increases much faster than length increase. Like as length doubles, mass squares.

So as fish get longer, in general their mass increases much more rapidly. As their mass grows, their oxygen needs grow to but much more slowly (though at a faster pace than their length increases).

As the details double, my headache triples.

Now, if only API made a water test kit that measured how happy our fish are!

 

[Mystery]

Well, the issue of welfare considerations is going to grow and grow too. I see it coming down the pipe--I just hope the upside will be getting rid of egregious abuses like Walmart bettas in little jars.