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Old 09-26-2005, 09:48 AM   #1
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The 1 inch per gallon rule - A discussion

There are alot of questions about when an aquarium becomes overstocked. IMO the above rule is something that's easily misunderstood. Especially to new hobbyists. Every species has it's own specific needs. The hobbyist that truly wants to provide his/her fish with the best possible environment needs to apply common sense to what has been a hobbyists guideline for longer than I can remember.

Obviously a 10 inch Oscar cannot be safely kept in a 10 gallon tank. However, 10 inches of neon tetras could. I'm curious what people think can be done to stretch the rule, and where the limits end?

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Old 09-26-2005, 10:49 AM   #2
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Having a fair amount of live plants can help, in terms of providing hiding spaces when you have some more aggressive species (like cichlids). They also provide extra filtration...and a buffer from ammonia spikes since plants LOVE to use the nitrogen in ammonia for a food source.

But I think the distinction between overstocked and overcrowded has to be made. You can have a tank that's overcrowded - not enough swimming space for each fish, while still having an adequate bio-filter that can handle the bio-load. But fish health will still suffer due to stress/aggression.

So to me, when you hit an overcrowded state, that's definitely a cut-off point for stocking.
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Old 09-26-2005, 10:57 AM   #3
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I honestly feel the rule is a great place for beginners to start... and continue to learn from. I also feel its a good marker of what you can and can't do with a tank, but with that being said, there are tons of other factors that come into play that are really the deciding factor.
For example, in my 75gal I can have roughly 75 inches of fish... give or take about 10-15in because I have the space and adequate filtration as well as plants. My boyfriend, on the other hand, has a 29gal with maybe 15in of fish... but he doesn't have much room for anything else due to aggression and swimming space. But, we both keep that rule kinda in the back of our minds and then apply common sense.

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Old 09-26-2005, 12:06 PM   #4
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We have a new article in the Articles Section that goes through this in great detail. Please take a look at it.

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Old 09-26-2005, 12:19 PM   #5
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I think that the "1 inch per gallon" rule is a good starting point for newbies interested in a peaceful community tank populated with small-bodied fish like livebearers, danios, rasboras, tetras, barbs, and most peaceful catfish.
It is NOT a good rule-of-thumb for aquarists interested in goldfish, cichlids, loaches, and agressive catfish.

In addition:

1) Use the ADULT fish length when applying it. Either that, or have a larger tank ready when the fish grow up. My 8 tiger barbs were 1/2 inch when I bought them; they're now 2 inches.

2) Realize that the rule is no longer adequate for very long fish, or stout-bodied fish like many cichlids. This is where swimming space and filtration requirements render the rule useless.

3) Realize that species-specific requirements take precedence. Aggression, territorial needs, and adequate hiding places may distort the rule.

I agree with Malkore that you can push the envelope a bit if you have alot of plants - but not by much...maybe by one or two extra fish.
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Old 09-26-2005, 12:55 PM   #6
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Originally Posted by QTOFFER
I agree with Malkore that you can push the envelope a bit if you have alot of plants - but not by much...maybe by one or two extra fish.
I do not recommend it, but I have done so by an extra 100%+ in a very heavily-planted, seasoned aquarium with relatively massive biological filtration and very frequent water changes.....but such a thing is so labour, space, and cost intensive, that its nothing anyone would likely ever want to try versus simply upgrading to a larger aquarium.
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Old 09-26-2005, 01:51 PM   #7
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The more you over populate or even bring it up to the rule with say Neon Tetras, you will have more work to do cleaning and changing water. After a year or two many people will tire of this and sell the aquarium. Or let the Nitrates build for for a year or more by just adding water as it is needed, because they no longer have time or want to expend time on the aquarium.

If you keep the load down to half or less of what it might be, much less cleaning, much less changing water and people who do this seem to keep their aquariums for a long long time. Of course there are exceptions to every rule, I know of one aquarist who keeps Oscars and does a 50% water change daily. He is very successful, but he is wholly into aquariums and nothing else. And has had them more than 10 years of course some ot the Oscars have been replaced.

I prefer to sit back and just watch the fish glide around the tank swimming in and out caves, fake plants which they seem to thoroughly enjoy. The less work the better I enjoy my aquariums.

Everyone is different, but this is something a beginner needs to think about. When I started I loaded the tanks to the max and started more and more tanks. The work soon became overwhelming and was taking time from my other hobbies, so I let some of the fish die of old age and transferred all the rest into one tank and let them die down to half a tank load and the joy of being an aquarist returned. When they all died off, I cleaned the tank, got a new XP3 filter, had a good start when disaster struck when I followed the directions that came with the filter, I knew better and questioned rinsing some of the filter ingredients with tap water. But I went a head and did it and it killed off all the bacteria in the bacteria converter and I used a new brand of ammonia converting chemicals and it was disaster. Lost most of a 90 gal tank with 9 Tiger Barbs, 5 Pink Tinfoils and two Paradise fish.

I moved all the survivors to my 29 gal tank. Two tigers actually are going strong and the Paradise fish are great. I had three Tigers but two attacked the weaker one and removed its tail fins and it died. But for some reason they did not bother my 5 platies, the 4 danios but they did in my Chinese Algae Eater, (may have been the Paradise Fish) and I have since added 3 more Tigers and now they bother no one just chase each other around my 29 gallon tank which has 20 inches of fish, more than I would like in the tank, but it was the only rescue tank available and it had been running so long it accepted everything with no ammonia spike even the addition of the 3 new Tigers. I do 10 gal water changes every 2 weeks and vac the gravel.

I add water often as necessary to replace the evaporated water and I measure the water parameters daily until I see how everything will work out. The Platies are very old and so are the remaining Zebra Danios. so I expect the fish load over all to gradually go down until I just have the Tigers and the Paradise fish in this 29 gal tank
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Old 10-01-2005, 03:16 AM   #8
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I have a ten gallon tank with a bunch of baby Marigold Swordtails, and some plants as well. What was happening, eventhough I do water changes every week, is that the waste was starting to take it's toll on the plants. I can see it in the way the plants are looking.

In my other ten gallon tank, I also had 31 baby Marigold Swordtails with a couple other fish, and the waste eventually killed my Mondo Green Grass. Now that I got rid of these fish, and did a major water change (5 gal. of water), the plants are just starting to recover. I see new leaves coming out of them, but lots of algae accumulating. So tonight I replaced the carbons, and will do my weekly water change as usual this weekend.

It just goes to show that the plants will only take so much before they have had enough.

A few more than 1 inch of fish per gallon didn't do any harm until my livebearers got horny.
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Old 10-01-2005, 04:18 PM   #9
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Personally I have a problem when people blow thier tops when someone puts per say a 3 inch tang in his 55 gallon tank. Sure, eventually that tang may get 8-12 inches in size and need 100 gallons + to accomodate it, but tangs grow very slowly and that person could get a year or more enjoyment and entertainment out of that fish before it really needs a much larger tank. When the fish gets too big, donate it to a zoo, fish store, private party - etc... I do think the 1 inch per gallon rule is dangerous to follow, and fish habits, waste production and more all need taken into consideration.
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Old 10-01-2005, 07:52 PM   #10
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I have never used or considered using the 1in per gallon rule. Its not that I have anything against it (though if you put 20 gold fish in a 20gallon tank I may take issue with that) its just never been a factor in my deciding what fish or how many I want. I don't look in my tank and think, great I have X number of free inches left to fill. I guess I like to play things on the safe side by understocking rather than worrying about trying to cram as many fish as I can into one tank. Granted my tank at the moment looks pretty bare and I will end up with more fish eventually, but when I do, the 1in rule probably wont come into play.
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Old 10-01-2005, 08:06 PM   #11
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I always thought for the most part that the one inch per gallon rule was very much an exageration of what could be put into a tank stockwise.. Of course UGF's were all the rage when I first started stocking my first tank, and for lack of any other filter I had about 10 cycles per hour of filtration from my HOB (back then I thought that 5 cycles was enough for any stocking arangement). Granted.. I was given the task of QTing a very large, very aggessive cichlid with my first tank (about 10 inches long) in a 48 gallon octagon, so the 10 cycles per hour was most likely nessisary to clean up after the fish in question. This is the extent of my experince with overstocked tanks really IMHO. And I really never looked back..

"understocking" prodused much better results in growth and health of my fish there after (two angel fish in a 40 long was my next tank) and that experince has sold me on oversizing the tank for the fish. Not that it cant be done.. It just seems to me that once the fish grow to there FULL potential in an "understocked" tank it makes it worthwhile IMHO.
Im not sure if this post is even on topic.. I hope it at least helps to explain my oppinon on this subject in general. :P
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Old 10-01-2005, 08:16 PM   #12
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side note: by "understocked" Im trying to say a tank that sutes the needs of the species in question to attain there maxium potential size in captivity.. this seems to be most benificial in my experiance for keeping healthy fish. this could mean more or less then the 1inch per gallon rule.. but in most cases.. its much less..
this of course takes in consideration how long you plan on keeping the fish (I assume fish are pets and will be kept for there natural life span with this stocking advice, adjust accordingly if you wish)
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Old 10-01-2005, 10:09 PM   #13
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I think a tank with one inch per gallon always looks crowded. In fact, the tank looks crowded at 0.75 inch per gallon. A tank that is too busy detracts from the individual beauty and character of each species. My current community tank fits this description, and I will eventually put some of these fish in another tank for aesthetic reasons. But it is not "overstocked" from a technical point of view, since filtration and water changes keep it pristine. That is with 40% water change one to two times a week, because I have plumbing to make the water changes a snap. If I had to drag out a python twice a week I would be miserable, and really regret it. Non aquarium owners love the look of this tank, because their idea of a fish tank is to see it teeming with life when you glance at it. That is what the one inch per gallon rule serves, the notion that a fish tank should be teeming with life at a glance. Possible to do, but after a while I bet most aquarium owners naturally drift to a much lower stocking level.
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