Inch Per Gallon Or Cm Per Litre?

[Tolak]

Everyone oversimplifies this "rule", which is not a rule, only a guideline. In aquatics, there are no rules, whatever works for one person may not work for another, there are so many variables that it's near impossible to have a list of set rules.

The entire guideline is 1" of slim bodied fish which grow to no larger than 3", per gallon of water.

 

[Bignose]

It's one SQUARE inch per gallon, people. A 20 inch aro will not fit in a 20G. Better to understock than overstock.

This doesn't make too much sense... how do you measure a square inch of fish? is it length times width or length times height or width times height?

If anything, like I said above, the most important factor would be the mass or volume of the fish.

Also, I didn't mention it above, but the surface area of the tank is an important consideration, too. A tall skinny 20 gal tank is very different than a long shallow 20 gallon tank.

Arguing over the specifics of the rule is kind of silly anyway -- there are too many factors that cannot be summed up into one simple phrase "x units per volume" -- very rarely is anything in life so simple and fishkeeping is no exception.

 

[Tolak]

Also, I didn't mention it above, but the surface area of the tank is an important consideration, too. A tall skinny 20 gal tank is very different than a long shallow 20 gallon tank.

Arguing over the specifics of the rule is kind of silly anyway -- there are too many factors that cannot be summed up into one simple phrase "x units per volume" -- very rarely is anything in life so simple and fishkeeping is no exception.

Again, this is to keep the beginning aquarist on safe ground at first, and would apply to a 20 long or a 20 high. IMO, in either case it is way understocked, which is a good start for someone who is just learning.

The 1"/gallon thing reminds me of the sort of thing you teach to kids, like crossing the street, "look to the left, look to the right, cross at the corner, walk with the light". I know as an adult, someone experienced with street crossing, that I have crossed against the light, crossed in the middle of the street, but I do generally look both directions for oncoming traffic. The 1"/g guideline is really no different as I see it, a safe start.

 

[geo7x]

I would advise newbies to start off with the 1" per gallon rule, but after a few months experience then it could be doubled.
I personally don't really go by any rule, just whether it looks right or not, but it usually ends up at about 2" per gallon for me.

 

[groovitudedude]

It's one SQUARE inch per gallon, people. A 20 inch aro will not fit in a 20G. Better to understock than overstock.

This doesn't make too much sense... how do you measure a square inch of fish? is it length times width or length times height or width times height?

If anything, like I said above, the most important factor would be the mass or volume of the fish.

Also, I didn't mention it above, but the surface area of the tank is an important consideration, too. A tall skinny 20 gal tank is very different than a long shallow 20 gallon tank.

Arguing over the specifics of the rule is kind of silly anyway -- there are too many factors that cannot be summed up into one simple phrase "x units per volume" -- very rarely is anything in life so simple and fishkeeping is no exception.

Yes, it does. If you have a 4 inch kuhli loach, and he's only 1/2 an inch thick, then he adds another 2 gallons. The 1 inch /gallon rule is for noobs who don't research their fish.

And yes, I agree. There are too many factors. That same kuhli loach would not fit in a 2G anyway! AND if you have 8 kuhlis, it's gonna be worse for the tank than if you have 4 kuhli loaches and 4 zebra danios.

 

[Bignose]

It's one SQUARE inch per gallon, people. A 20 inch aro will not fit in a 20G. Better to understock than overstock.

This doesn't make too much sense... how do you measure a square inch of fish? is it length times width or length times height or width times height?

If anything, like I said above, the most important factor would be the mass or volume of the fish.

Also, I didn't mention it above, but the surface area of the tank is an important consideration, too. A tall skinny 20 gal tank is very different than a long shallow 20 gallon tank.

Arguing over the specifics of the rule is kind of silly anyway -- there are too many factors that cannot be summed up into one simple phrase "x units per volume" -- very rarely is anything in life so simple and fishkeeping is no exception.

Yes, it does. If you have a 4 inch kuhli loach, and he's only 1/2 an inch thick, then he adds another 2 gallons. The 1 inch /gallon rule is for noobs who don't research their fish.

And yes, I agree. There are too many factors. That same kuhli loach would not fit in a 2G anyway! AND if you have 8 kuhlis, it's gonna be worse for the tank than if you have 4 kuhli loaches and 4 zebra danios.

No, it doesn't make sense. You didn't (directly) answer my question, but from your example, you intend that length x width is the area you mean.

Well, let's look at some examples, then. Compare the common hatchet fish ( http/www.fishprofiles.com/files/profiles/370.htm )and the zebra danio ( http/www.fishprofiles.com/files/profiles/484.htm ). They are both pretty close to the same length, 2 inches, and both a very slim bodied fish, so your area measure, length x width says that they are equal --- but the hatchet fish is probably three times the height as the zebra danio, the hatchetfish is probably at least three times the volume of the zebrafish, and it's deep body is actually large pectoral muscles that the hatchet fish uses to glide up out of the water. Both are fast swimmers, but the use of those large muscles means even more waste is going to be produced as the muscles use the food energy the hatchetfish takes in.

We can even compare a third fish, the peppered cory catfish ( http/www.fishprofiles.com/files/profiles/386.htm ). Now, it is the same length, but it is very thick-bodied. By your measure, it would be the biggest waste producer of all. But, that simply isn't true because the other two above are very active fish, constantly moving about. The peppered cory is a pretty shy catfish, and spends a lot of its time sitting on the bottom of the tank not moving at all.

We do agree on that there are more variables than can be taking into account by just a simple measure, but any area measure is going to be as inherently flawed as any length measure is.

Not only that, but the amount of waste a fish produces is proportional to its mass, which is proportional to its volume. Length times width time height is a much better measure than any area or length measure. It isn't perfect, either, no where near really. Again, all those additional variable I've mentioned in my above posts. But, LxWxH is far better than any length or area measure because it takes the whole fish into account, not any arbitrary choice. Fish are diverse enough that I can always find examples where length is poor descriptor, and I can always find examples that LxW is a poor descriptor. The other nice thing is that LxWxH is related to the nature of the waste production of the fish. Again, the amount of waste a fish produces (and similarly the amount of oxygen a fish needs and the amount of food a fish needs) is related to its mass. And that is going to be related to its volume, so LxWxH is more closely related to the actual physics/chemistry of the situation than length or area is. The real problem is that LxWxH or mass is hard to measure. (So is an area for that matter.) That's why the length measure has retianed its popularity. It is not tough to get a good estimate of a fish's head to tail length, but estimating its thickness and height can be tough, and little mistakes add up. If you accidentally call a fish that is 3/8 inch only 1/4 inch thick, then you could end up putting a lot more fish in a tank than is healthy.

Anywoo, I hope that this long post and long thread has convinced anyone else that reads this thread that 1 inch per gallon is a poor rule that does not take into account many, many other factors. But, it is as good a starting place as any, especially for inexperienced fishkeepers.

 

[rdd1952]

Lizzie, as mentioned, the 1" thing is a guide. It is great for beginners to help them learn what to look for and keep the tank stable while it matures. It can easily be exceeded later. There are a couple things to consider with your stock list that will impact your stock level later on. With female livebearers, you will constantly be adding more and more fish. So even if you only have the 6 x-ray tetras, 3 guppies, 3 platys and 5 corydoras, in 3 to 6 months, you will most likely at least double that with additional platys and guppies.

 

[Lizzie71]

I won't have fry. My female platys have been with me for nearly 6 months now and are not pregnant - we did have fry from one of them in the first couple of months but none for 3 months now.

And the guppies will be all male.

 

[MHunt]

if you go on the Practical Fishkeeping calculator, it takes into account the volume of the tank you are stocking, and normally comes out saying 1" per gallon to begin with, then 2" per gallon after say 6 months once the tank and filters are properly mature. But as has been mentioned above, these are all grand simplifications to keep beginners generally out of trouble. Your best bet is to research the fish you are planning to stock and see what kind of tank size requirements they have also.

 

[groovitudedude]

I guess it's a good thing that I'm not an idiot then, huh Bignose?

 

[OohFeeshy]

This doesn't make too much sense... how do you measure a square inch of fish?

Silly... you hit it with a rolling pin until it's wafer thin, draw round the mess on some squared paper and count the number of squares it takes up... Easy.

Yes, it does. If you have a 4 inch kuhli loach, and he's only 1/2 an inch thick, then he adds another 2 gallons. The 1 inch /gallon rule is for noobs who don't research their fish.

And yes, I agree. There are too many factors. That same kuhli loach would not fit in a 2G anyway! AND if you have 8 kuhlis, it's gonna be worse for the tank than if you have 4 kuhli loaches and 4 zebra danios.

Some very strange mathematics there... Evidently you haven't the faintest idea about what kuhlis are like... Very bendy, very low waste producers, very thin, probably not even 4" long at maximum...

 

[rdd1952]

This doesn't make too much sense... how do you measure a square inch of fish?

Silly... you hit it with a rolling pin until it's wafer thin, draw round the mess on some squared paper and count the number of squares it takes up... Easy.

I can see how that would work. Then you could just blow them back up with a bicycle pump and stick them back in the tank.

Yes, it does. If you have a 4 inch kuhli loach, and he's only 1/2 an inch thick, then he adds another 2 gallons. The 1 inch /gallon rule is for noobs who don't research their fish.

And yes, I agree. There are too many factors. That same kuhli loach would not fit in a 2G anyway! AND if you have 8 kuhlis, it's gonna be worse for the tank than if you have 4 kuhli loaches and 4 zebra danios.

Some very strange mathematics there... Evidently you haven't the faintest idea about what kuhlis are like... Very bendy, very low waste producers, very thin, probably not even 4" long at maximum...

But even if you did use the cubic inch thing, a 1/2' inch high/thick fish that is 4" long would only account for one gallon of water and not 2.

.5 x .5 x 4 = 1

 

[Bignose]

I guess it's a good thing that I'm not an idiot then, huh Bignose?

I never called you an idiot, or even anything like it.

I am just pointing out that both length and area have similar weaknesses. Volume is a much better measure of how much waste a fish is going to produce. It isn't anywhere near perfect either, because it doesn't take into account how active a fish is, or how a certain fish's metabolism is defined. But, it doesn't suffer mistakes from the odd-shaped fish nearly as much as a length or an area measure will. Though volume is a very impractical measure, because it is harder to get accurate heights and thicknesses of the fish.

I never intentionally insult someone. I am just trying to point out that area isn't really significantly better than length. #1 it still gives funny results for fish that are shaped differently and #2 it is much, much harder to measure a thickness of the fish accurately. The difference between 1/2 and 3/4 of an inch become huge when you start multiplying them, and could change what you think the stocking is or calculated to be. So, in conclusion, area per gallon isn't really much of an improvement. That's all I was saying.

p.s. not to mention, I am curious where you got the idea from. Was it in a book/magazine/webpage? If it was, could you cite it for me? The reason I ask is because I've seen many sources talk about stocking in terms of length of fish per unit surface area of the top of the tank, but never a rule with area of fish per unit volume.

p.p.s. if you think it is such a superior system, why don't address some of the point I raised, rather than worrying about namecalling? If you have some really compelling reasons why area per volume is a far superior method, I'd like to hear them. I fully acknowledge that I could have very easily overlooked something. So, if you have some reasons, please bring them to the table rather than thinking I insulted you or trying to insult me.

 

[Tolak]

I have seen medication dosages based on fish weight, but not by volume. Perhaps this could be taken into account somewhat, discounting or weighted against the particular fish's metabolism or diet.

With smaller aquarium fish you would be dealing with grams, or fractions of grams. I know in Nelson Herzog's book on medications used for fish, some medications are based on kg of fish, which usually means either a fish farm situation, or larger fish in a public aquarium, though I know we have a few members with kg+ size fish.

 

[Bignose]

Weight and volume as pretty much the same thing in this case. A fish's density is just a hair over 1000 kg/m^3 (the density of water) -- and it would not be a huge error to just assume the same density as water. So, if you have the wight of the fish, you can always convert it to volume and back.