Fish per gallon rule?


I have read and heard many different versions,anywhere from 1" per 2gl up to 1" per 5gl. I wust just wondering what every1 bases theres on.


I have read that each inch of fish requires 48 sq/in of surface area. This seems a bit much for real estates since my tank is a 45 gal. fish only and I have 5 fish. Regal Tang (1.75"), Royal Gramma (2"), Blue Devil (1.5"), Fire Fish (2") and a Perc (2"). It took me a while to measure them since they wouldn't stand still so I guesstimated. This is close to what the "Books" recommend. I have had more fish in here (at one time) but they died (probably due to lack of surface area. :D ).
Just remember to gradually add your fish. Don't add a bunch all at once. It could stress the tanks balance.
Good luck.


So what's up with this company SWF selling you these reef packages with 6-7 fish in it?! I'd love to get one in a month or so, but then I'd feel stupid if some died on me b/c of ammo, etc. Any thoughts?! :confused:


I personally think that the fish per gallon rule is the most stupid rule ever thought up. More importantly you should ask yourself questions about your own tank, since everyones aquarium can be unique.
Are there enough hiding spaces for that fish?
Can my filtration handle more fish?
Is the fish territorial?
Is the fish compatible with the ones I already have?
Will the fish Grow to big for my tank?
What does this fish eat? messy eater?(Puffers)
How much time do i want to spend on maintaining a "full bioload"?
There are so many things to consider nobody can tell you what is right or wrong without knowing exactly what your tank is like in so many aspects. You need to use your better judgement when making the decision to add more fish and read about the ones your intersted in. Never take a risk and say "we'll just see how it works out", unless your willing to pay the consiquences.
Good luck


Staff member
Well said, Orby and exactly right! Throw out the old "per inch" formula used for the FW hobby and think more conscientiously when setting up your marine system. Consider each fish's needs and then consider the needs of the community of fish you plan to stock your tank with. Doing so will make for happy, healthy fish, and an even happier hobbyst!


Sammy and Beth are right!! Also you can see where the fish you already have like to swim, if they always hoover in one spot, or do they like the bottom or the middle. They kinda get their space in the tank, if you add to many fish suddenly each fish doesn't get it's own space. I definitley think the hiding spaces are important to. Most fish like to hide somewhere at night to sleep, just like us we go to our beds at night, the fish go to theirs. So if you have 5 fish it is a good idea to have 5 "beds." Each one of my fish has their own little spot to sleep, some in the barnacle, another in a rock hole, and one in a coral hole, ect... but they each have their own personal space.

nomar g

New Member
I agree with the aforementioned posts re the inches per gal. rule but some type of basic guideline is necessary to keep newbies out of trouble. As long as the ratio is on the conservative side, say 4 or 5 gal. per inch of fish, it can serve a useful purpose.


Hey!! I represent...I mean resent that comment about newbies.... :D


I really dont think that the fish per gallon rule is a good one. It depends on type of fish and type of the tank cuz taller tanks would not be as good for a fish that likes to pace around in the tank cuz it can only go up and down.

nomar g

New Member
You have to consider the size the fish is likely to reach in your tank. The capacity of the tank and the way you maintain the fish may limit the maximum size the fish will attain but to be on the cautious side, you should assume your fish will reach the maximum size estimated by experts in books such as S. Michael's Marine Fishes, a pocket guide.