Julienlore

I've started cycling my tank and have "designed" the final product I intend to keep. I know of the inch per gallon rule, but was wondering a few things regarding this rule. I DON'T intend to overstock - this is mearly a curiosity.

1. Is this rule derived from the amount of filtering a given size tank can handle? This doesn't make much sense since a lot of the bio filtering is within the filter and increasing the filter would allow for more bacteria. My 20 gallon tank has a 40 gallon Aqua Clear filter, for example. Also, a planted aquarium has a bigger "bio" filtering capacity.

2. Is the rule based on the amount of "room" a fish needs to swim in a tank or territory one occupies? Since most fish vary in behavior, this would change on a "fish" basis. Also, most fish occupy different strata in a tank. Keeping some top level fish with bottom dwellers would not interfere with this.

Just wondering what are the foundations of this "rule",

Julien

Dino

At best it is a general guess.

Or as I like to think it, the lazy way out.

As you mentioned it has lots of holes.

It is supposed to be a combination of fish size, territoriality, activity level, and the amount of waste most fish produce.

And, sorry to be a bit negative, it is supposed to be for adult fish. But most people use the size the fish is at the present, which causes all types of problems.

sirdarksol

I prefer to think of this as a guideline. It works in some cases, but in others it doesn't.
It does concern swimming room to some extent, but some fish are more or less aggressive than others, or require larger swimming areas, so this can be modified. For example, guppies are small, yet it is suggested that they be kept in a tank no smaller than 20g.
It also concerns bioload. No matter how good your filtration is, it doesn't actually remove waste from the water, it just turns it into something less toxic. Less toxic, however, doesn't mean non-toxic, and fish will eventually suffocate in the by-products of this waste conversion. The smaller the tank, and the more fish in it, the faster this will happen.
There are a few things that will break the guideline. Particularly large critters have a vastly increased impact and particularly small critters don't have terribly much effect on the bioload. For example, I probably have about thirty inches of small Malaysian snails in a 10g tank, in addition to the three inches of betta in the tank. But waste production really has more to do with mass than length, and there probably is more mass of betta than there is of snail. Conversely, large fish, such as an oscar, or fish that have more mass per inch, produce far more waste than their inches would suggest (this fish also usually need more swimming room).
Another factor is type of fish. Depending on general diet and other things, some fish produce more waste than others. goldfish, koi, and plecos, for example, are all very messy fish.
I usually consider the guideline for more common aquarium fish, tetras, mollies, cories, otos, bettas, platies, etc... When you get into bigger fish like oscars, large cichlids, and such, they require far more research and care, and a simple, "lazy way out" guideline like this really doesn't cover it anymore.

Julienlore

It seems to me that waste producst and bioload would be influenced by live plants. For example, a heavily planted aquarium with healthy growth would consume more nitrates reducing the levels in the tank. I have a nitrate testing kit and will keep an eye on the levels at first.

Do people include snails in these calculations?

Julien

voiceless_kat

Following the inch per gallon rule, at this beginning point, I have only 46 " of fish in my 55g.Thanks CWC) However, there are still 4 guppies to go in a 3 otos.

At first, I thought it looked empty, and I kept thinking of all the different fish I would still like to have.

However, only 5 days into it, The 46 inches of fish looks so nice, with everyone having plenty of room. Once the live plants , the gups and otos are in, it will surely be perfect.....I think too many fish in a tank wouldn't look as nice. Leaving more room shows off the fish more, the decorations, the whole thing. IMO less is more. ( Geez, could I be more scientific??)

Val

sirdarksol

Yes, you're right, live plants will influence the bioload, as long as they remain healthy. However, they will also have a negative impact on swimming space. Again, this is just a basic guideline, not meant to encompass every possibility.

(Dino really has it right, it's kind of the lazy way out)

COBettaCouple

i view the 1" adult size per gallon as a minimum requirement since quite a few fish produce excess waste and/or need more room to swim (like a 12" fish will need way more than 12 gallons). Flaws include allowances for plants, fish that grow to large sizes and the fact that a 10 gallon tank will have less than 10 gallons in it, with substrata, etc.

If your fish are all going to be 6" or less, it's a lazy but fairly good way to keep a tank from becoming a death trap of fish waste. If any fish are going to go over 6", then they'll probably need at least 3 gallons per inch (adult size). So a common Pleco (18") would need 54 gallons, which rounds to 55g since that's the next common tank size.

I'd still research any fish for space needs, as there are small fish needing 3 gallons per inch, like Dwarf Puffers.