# How many fish? Do old rules not apply to planted tanks?



## zavikan (Jan 5, 2009)

I saw some one on here with a 40-50 gallon heavily planted tank, with over 80 fish in it. No one seemed to explode on him, so I was wondering if this is normal?

I have a 38 Gal tank, with 19 fish in it. (10 are 2 different tetra schools). The old rule used to be basicly around this ratio. With so much plant cover, is this kind of out the window?

I would love to add to my schools and 2-4 solo guys, but have held back because I want happy fish.


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## Homer_Simpson (May 10, 2007)

zavikan said:


> I saw some one on here with a 40-50 gallon heavily planted tank, with over 80 fish in it. No one seemed to explode on him, so I was wondering if this is normal?
> 
> I have a 38 Gal tank, with 19 fish in it. (10 are 2 different tetra schools). The old rule used to be basicly around this ratio. With so much plant cover, is this kind of out the window?
> 
> I would love to add to my schools and 2-4 solo guys, but have held back because I want happy fish.


I am sure others way disagree, but based on my experience with what I have seen with my planted tanks. 1/2" fish per gallon which is even less than the 1"/fish per gallon rule works best for happier, healthier, fish that appear to peacefully exist. Other factors come into play and are just as important, such as finding a balance of top dwelling, mid dwelling and bottom dwelling fish when you stock. The belief that one can overstock a tank that is heavily planted and the dense mass of plants will compensate for overstocking is nothing more than a myth in my experience. I tried this with a tank and it proved disasterous, to say the least.


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## newshound (May 9, 2005)

I 2nd homer!


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## monkeyruler90 (Apr 13, 2008)

sure, 20 people can fit in a 11X16 room but i dont think they would be as happy.

if you lightly stock the tank the inhabitants are going to be happier and show better colors. thats more worth it than having a ton of ugly raggety fish.
i try and stick to the 1inch per gallon. but with neon tetras i overstock by 2 or 3 more fish, but thats it.

oh and also, im not 100% how much otos and shrimp add to the stocking levels. anyone want to explain that part?


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## o snap its eric (Jan 12, 2004)

stocking fish has to do with your filtration and water upkeep. You can keep as many fish in your tank as you want as long as you can maintain your water parameters Remember, these community fish have very sort term memory by the time they swim across the tank they have pretty much forgotten everything. 1" per gallon is not a rule but rather a yardstick in fish keeping. I have two tanks, a 200g predatory fish tank and a 60g planted tank. My predatory tank consist of a 16" male umbee, 20" black aro, 8" frt, 10" aba all growing fast and showing great color however it's starting to get cramped and if i was going according to the 1" per gallon rule i should be fine for a long time but i'm not. I will have to upgrade soon due to aggression and space to swim. 

With my planted tank, i have 13 rummy nose, 7 cardinals, 2 ottos, 2 black mollies, 3 amano shrimps all averaging about an inch all doing fine as well but its boarder lining crowding in my opinion. If i was going with the 1" per gallon saying then i should be able to keep 60 1" fish in my 60g. That would be massive overcrowding with all the plants in the tank and while technically i can keep them in good health i will need a powerful filtration system and multiple water changes a week to ensure their good health. 

So again, it's not the limit of number of fish you should be concerned about, it's if you can keep the water in check.


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## lauraleellbp (Feb 3, 2008)

^^ I absolutely agree.

Another thing to keep in mind beyond water parameters is that different species react differently to crowding. Small schooling tetras actually love being crowded, the more, the safer they feel.

Other species such as swordtails need their space- and tend to become aggressive towards each other (and often tank mates as well) when overcrowded.

"Can" and "should" are two very different things. 

Personally, I understock. I like being able to leave on vacation for a week or two and know that my tanks are completely fine all on their own, even without water changes, and maybe someone popping in once or twice to feed and make sure the electricity hasn't gone out or something drastic like that.


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## AlaskanCorydoras (Jan 1, 2009)

Laura is spot on. . . there are other considerations to contend with. If you are going with the inch of fish rule, you could easily end up with 50 tetras in a 55 gallon tank. In truth they'd be quite happy like that. they'd even likely tolerate even more, being a strong schooling fish. On top of that popping some corys in wouldn't impact the balance all that much, as they'd help with cleanup, not to mention an oto or two. . . 

OTOH if you did a similar stock with GBRs they's all flip out and go psycho on each other: They DEMAND more room than tetras do. 30 gbrs in a 55 gallon tank would be both amusing and tragic to watch.

In short, if you have sufficient filtration in the tank (And plants count towards this) you CAN overstock. However this makes the entire tank more fragile. Further some species tolerate being overstocked more than others.


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## annette (Jun 18, 2008)

I think you can put more in there than you definately have now, but don't over do
it, crowded conditions cause stress, stress causes ick. I have a heavy planted 20 gal tank and I have 3 schools, one of rummy nose-10, one of neon's-10 and one of von rio tetras-8 about 28 fish. A few less now as I had a water problem and lost about 3 or 4 of my fish. Mine were added gradually and I would never put more in there at this
point because technically I probably have too many in there now but I do frequent water
changes and its been working for me. pick a few schooling fish you really like and build up those schools. Its beautiful to watch a large school of something swimming around your tank.


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## Homer_Simpson (May 10, 2007)

Number of fish, types(top dwelling, mid dwelling, and bottom dwelling) of fish, compatibility, individual temperment differences, filtration, and frequency of water changes are all inter-related. Hell, even the rate and amount the fish poop can make a significant difference. A heavy pooper like a pleco added to a small tank where stocking levels are already pushed to the max could easily tilt the balance for the worse. The number of fish IME does make a difference, regardless of filtration, plant density, and frequency of water changes. You can overcrowd a tank and assume that it is okay because you heavily plant, have superduper filtration, and do frequent water changes. But this misses the point, just by the very act of overcrowding, you are creating a situation where fish will get into constant territorial sparring and some fish will get seriously stressed and injured. This opens up the door way to weakened immune system and greater susceptability to illness. Many people assume that the only reason overcrowding a tank is bad is because you need to feed more, which results in more fish poop and waste. Folks assume that this is easily resolved by heavily planting a tank, minimal feeding, heavily planting, having super duper filtration, and doing frequent water changes, but this misses the whole point of fish stress caused by overcrowding and the subsequent territorial sparring and possible life threatening injuries.


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## cjp999 (Nov 18, 2008)

annette said:


> crowded conditions cause stress, stress causes ick.


Not true. Ick is a parasite. If it is present in any amount in your tank, you'll know because most fish will show signs quickly. Ick won't wait for stress before it shows up. Stress can cause ick to kill off your fish faster. If your tank gets ick, the survival rate will be much better if the fish were happy and healthy to start with. But stress won't cause ick, nor will lack of stress prevent it.

On the other hand there are many types of bacterial and fungal infections that fish can get when stressed because the bacteria or fungus causing the infection are always present. This is like picking getting an infection after a cut. No one passed the infection on to you. It is caused by bacteria that are always present and are just taking advantage of the situation.


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## flanders (May 3, 2008)

o snap its eric said:


> Remember, these community fish have very sort term memory by the time they swim across the tank they have pretty much forgotten everything.


Um....this is definitely a myth. Memory in fish has been extensively studied. In fact, recent work has shown that fish have similar memory capabilities as mammals.


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## kid creole (Dec 25, 2008)

flanders said:


> Um....this is definitely a myth. Memory in fish has been extensively studied. In fact, recent work has shown that fish have similar memory capabilities as mammals.


Here's a short note about a study:
http://www.thefishsite.com/fishnews/8707/study-fish-memory-may-lead-to-greener-farming

Also, I empirically know this is false because my fish know where I am going to drop the food, and also where the current is going to push it.


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## o snap its eric (Jan 12, 2004)

i agree and disagree about some of the points. Over stocking is subjective, in asian countries, fish are constantly "over stocked" in our eyes however in the asian culture they aren't. I've seen my fair share of weird combos.... some worked some didn't. But the weird thing is that they are able to sustain the fish for a long time and also keep them in good health. I admit, i'm relatively new to planted tank as my expertise lies with keeping predatory fish. With my experience and knowledge it's not the number of fish per say that is a crucial factor, it's how well you know the species of fish and how you can keep up the water chemistry. As you and some others have pointed out, knowing compatibility, health issues are a prerequisite to keeping any fish in a planted or predatory tank. Certainly don't want a dwarf pike cichlid in my tank full of cardinal tetras right? 

This thread turned out to be a great discussion. 




Homer_Simpson said:


> Number of fish, types(top dwelling, mid dwelling, and bottom dwelling) of fish, compatibility, individual temperment differences, filtration, and frequency of water changes are all inter-related. Hell, even the rate and amount the fish poop can make a significant difference. A heavy pooper like a pleco added to a small tank where stocking levels are already pushed to the max could easily tilt the balance for the worse. The number of fish IME does make a difference, regardless of filtration, plant density, and frequency of water changes. You can overcrowd a tank and assume that it is okay because you heavily plant, have superduper filtration, and do frequent water changes. But this misses the point, just by the very act of overcrowding, you are creating a situation where fish will get into constant territorial sparring and some fish will get seriously stressed and injured. This opens up the door way to weakened immune system and greater susceptability to illness. Many people assume that the only reason overcrowding a tank is bad is because you need to feed more, which results in more fish poop and waste. Folks assume that this is easily resolved by heavily planting a tank, minimal feeding, heavily planting, having super duper filtration, and doing frequent water changes, but this misses the whole point of fish stress caused by overcrowding and the subsequent territorial sparring and possible life threatening injuries.


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## Chartreuse Boots (Nov 16, 2007)

I don't think the old rules apply to any tank, planted or otherwise, not really as Rules anyway. That being said, they aren't completely useless as some would have you think. There are alot of limiting factors regarding a tank's capacity. Waste, territory, oxygen, physical space, exe. And it isn't enough just to say "stocking is complicated, inch per gallon doesn't work, overstocking is bad." what does that give us? Nothing! Not even a starting point! so we are stuck with the old rules, but we can't treat them as rules. Inch per gallon works well to estimate the waste production of small tropical fish, or atleast give us a starting point. If they are small messy fish, double it. For example you could keep 10 1" guppies in 10g or 2 2" goldfish. And the larger the fish is the more it multiplies; a full grown goldfish needs atleast 30g to himself, preferably in a pond. You could also keep 5 dwarf gourami in a 10g... If waste was your only concern. Since gourami are species agressive they will need atleast 15g per gourami. So you could keep 1 dwarf gourami and 8 guppies in a 10g or 2 dwarf gourami in a 30g with 26 guppies. Then, of course, you have the oxygen to worry about. This is ussually only a problem with planted tanks where co2 is added, surface turbulace is at a minimum, and plants are also absorbing oxygen at night. Under those circumstaces, the five gourami were better off than the two goldfish. Unfoutunately it' a bit harder to measure the oxygen a fish will use, and how much your tank has available. The best "rule" anyone has come up with for this is "guess and check". I find that a bit cruel for the fish though and usually try to steer towards air breathing fish for that sort of tank to prevent it from becoming a problem. As for plants affecting the waste capacity of a tank, there is varriation here too! A low light, low tech, heavily planted tank is not going to have the same waste absorption of a high light, co2 injected tank with even a few fast growing plants. I' d geuss in the right setup, the right plants could double, maybe triple the waste capcity of a tank! But test that at your own risk. Plants also help to create hiding spots and diffuse agression, but not really enough to excuse overstocking territorial fish. Finally there is physical space, theoreticly, with a flowthrough system, nonagressive fish, and cool water with plenty of surface turbulance, you could have unlimited fish... But not really. Fish can still get stressed from crowding the same way a human can in a crowded room. Even peaceful fish need to be able to get away from the other fish sometimes. This is an easy problem to aviod though as most of us run into a different limiting factor first, or have no desire to keep that many fish. 

And all of that is why most people use inch per gallon.
I apologize if that contains some errors, it was typed on a iPhone.


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## cjp999 (Nov 18, 2008)

I've been meaning to type up a similar reply to yours for a few days now. Although I'm still somewhat new to this, a lot of it is just common sense. Plants help deal with waste. Larger filters combined with more frequent water changes do the same. Plants, larger filters, and frequent water changes pretty much means waste won't factor into how heavily you stock your tank. You'll instead run into stress and compatibility issues before waste becomes a problem. This is where stocking your tank becomes more art than science, and years of experience certainly pays off a lot.


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## hokuryu (Jan 6, 2009)

lauraleellbp said:


> ^^ I absolutely agree.
> 
> Another thing to keep in mind beyond water parameters is that different species react differently to crowding. Small schooling tetras actually love being crowded, the more, the safer they feel.
> 
> ...


 Older thread, came to it on a search for vacation ideas, as we're heading out of town next month for 3-4 days, and I have no idea how I'm going to handle things. 1 20H, with a school of cardinals, 3 otos, 1 BN, several amanos, a small fry tank for 2 red wag platies, a 10G with several white clouds and a betta. I've thought about an autodosing setup, but I'm tapped for now on outlay. So I guess I'm stuck with trying to get someone to come in, or relying on an autofeeder for a few days, and, what, loading heavier on ferts on day 1 and hoping for the best? Anyway, the real thing I'm intrigued by here is the notion of stocking tetras heavier than other species - in my 20H, if all goes well, I only intend on a school of cardinals, my BN, otos, amanos. Would 13-15 be a reasonable amount of cardinals, or would you experienced tetra keepers advise this is too many?


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## Psittac (Jan 24, 2009)

cjp999 said:


> Not true. Ick is a parasite. If it is present in any amount in your tank, you'll know because most fish will show signs quickly. Ick won't wait for stress before it shows up. Stress can cause ick to kill off your fish faster. If your tank gets ick, the survival rate will be much better if the fish were happy and healthy to start with. But stress won't cause ick, nor will lack of stress prevent it.
> 
> On the other hand there are many types of bacterial and fungal infections that fish can get when stressed because the bacteria or fungus causing the infection are always present. This is like picking getting an infection after a cut. No one passed the infection on to you. It is caused by bacteria that are always present and are just taking advantage of the situation.


 
Ich is infact a parasite however it is present in every fish tank known, the only thing is it isn't active. Once a single fish becomes stressed and weakened they are then suseptible to the parasite, at this point the ich becomes active and spreads to the rest of the fish in the tank.


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## x2h (Dec 23, 2008)

i bet it will be fine for 3-4 day even if you leave them alone without a feeder. I've done that before for a week and they were fine and very happy to see me again!


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## Psittac (Jan 24, 2009)

Everyone has basicaly covered all of the factors that go into stocking a tank so all I have to say is it's best to simply watch your tank to figure out how well it's doing and adjust accordingly. I've only had tanks for a few years but I tend to change the quite frequently and I've gone through both ends of the spectrum. Being able to trade in fish any time you see fit is a huge benefit. It basically comes down to preference and whether or not your fish are going to be healthy. And at times the only way to know how well the tank will do is to try it and find out. So long as you watch your tank often enough, I've had tanks that every time I watched them they looked peacefull but every now and then I'd turn around and find an injured fish, and in an overstocked tank trying to find the culprit can be very difficult.

I've found that a very lightly stocked tank tends to be my preference now as it allows the fish to act more naturaly. IME upgrading to a larger tank shouldn't be a way to get more fish or bigger fish but to allow your fish the freedom of acting the way they prefer. Thats just what I enjoy watching however and even still I've got a tank thats simply a means to more and bigger fish. It's all preference and the debate should be raised as a way of keeping any fish keeper attentive to the state of their fish tank rather then improperly keeping fish and not even knowing it. The inch per gallon rule is simply a way to bring the topic up and put it on the minds of new fish keepers. After you've got an idea of what is acceptable just try it out and get a feel for whats right for you. I've seen both ends of the spectrums in my tanks and in the tanks of others and not one of us can say they're more correct then the other.


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## Psittac (Jan 24, 2009)

o snap its eric said:


> Remember, these community fish have very sort term memory by the time they swim across the tank they have pretty much forgotten everything.


I can think of several occasions that would prove this wrong.

After my black female angel died I tried several times to get my silver three stripe to pick another mate. He never did then one day I introduced two black angels from a QT tank and within days he picked one of them as a mate. You can't tell me he didn't think it was his old mate only smaller and different.


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## kid creole (Dec 25, 2008)

Psittac said:


> I can think of several occasions that would prove this wrong.
> 
> After my black female angel died I tried several times to get my silver three stripe to pick another mate. He never did then one day I introduced two black angels from a QT tank and within days he picked one of them as a mate. You can't tell me he didn't think it was his old mate only smaller and different.


Once you go black, you never.... oh never mind.


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## cjp999 (Nov 18, 2008)

Psittac said:


> Ich is infact a parasite however it is present in every fish tank known, the only thing is it isn't active. Once a single fish becomes stressed and weakened they are then suseptible to the parasite, at this point the ich becomes active and spreads to the rest of the fish in the tank.


I've created a new thread for this:

http://www.plantedtank.net/forums/fish/82287-can-ick-parasites-lurk-aquarium-indefinitely.html


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## Walking_Target (Jul 16, 2008)

I would say that no 'rule' applies 100% of the time. As Laura said above, Tetras (especially neons and that ilk) love large numbers, you can 'overstock' slightly and they'll be happier than pigs in crap. 

Then there are other species which merely tolerate crowding (Such as corys) where they do school, but they like their space too. 

Then there's the last class of fish, things like small Apistos, P. Pulchers and M. Ramezeri, which will merely put up with other (non mated) members of their species if crowded. 

The two *real* cardinal rules to remember;

1. More space is always better! (what better excuse to get a bigger tank?)

2. Know your species.


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## lauraleellbp (Feb 3, 2008)

I actually think "one gram of fish per gallon" is a bit of a better rule of thumb than one inch per gallon, since it incorporates body mass- but still, doesn't take into account any species-specific behavioral/environmental needs at all.


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## Kozy (Jan 30, 2009)

Also, I have to remind people a lot that 10 1-inch fish does not equal 1 10-inch fish when they bring it up. And to the OP, even if someone has that many fish, you do not know how much water they are changing either. 1/2 tank water changes sound fun.


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## cjp999 (Nov 18, 2008)

Kozy said:


> Also, I have to remind people a lot that 10 1-inch fish does not equal 1 10-inch fish when they bring it up. And to the OP, even if someone has that many fish, you do not know how much water they are changing either. 1/2 tank water changes sound fun.


Twice the length generally means 8x the mass, thus lauraleellbp suggestion to use mass instead of length. However, I have no idea how much my fish weight, but I know how big they are!

Also, if you assume relative spacings remain the same as fish get bigger (a fish 2x the length of another fish would want 2x the spacing between fish), then this also results in an 8x multiplier.

I think the 1" "rule" is generally meant for fish a typical novice would get, for which 1.5" to 3.5" is common length.


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## Kozy (Jan 30, 2009)

cjp999 said:


> Twice the length generally means 8x the mass, thus lauraleellbp suggestion to use mass instead of length. However, I have no idea how much my fish weight, but I know how big they are!
> 
> Also, if you assume relative spacings remain the same as fish get bigger (a fish 2x the length of another fish would want 2x the spacing between fish), then this also results in an 8x multiplier.
> 
> I think the 1" "rule" is generally meant for fish a typical novice would get, for which 1.5" to 3.5" is common length.


Its hard getting that through the heads of people who want 2 Oscars and a 10 gal kit.


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## cjp999 (Nov 18, 2008)

Kozy said:


> Its hard getting that through the heads of people who want 2 Oscars and a 10 gal kit.


When I said the 1" rule is generally meant for fish a typical novice *would* get, I should have said *should* get. Way to many end up cute little Oscars, Plecos, and Balas that will grow way to big. I don't blame the novice. The merchant is almost always to blame, especially the chain stores.


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## TheVisionary78 (Mar 6, 2010)

I just have a 29 heavily planted aquarium that is in a southern window with supplemental lights. As far as fish go I have 3 Octo cats, 2 Flying Foxes, 5 schooling Harlequin Rasboras and 2 platys I would actually like to get rid of. I calculated my aquarium size per inch of fish at 23. So I guess I could get more but I am holding off. My biggest problem is that my algae eating fish are running out of food so I either need to get rid of at least two of them or supplement with aglae waffers.


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## Noahma (Oct 18, 2009)

Walking_Target said:


> I would say that no 'rule' applies 100% of the time. As Laura said above, Tetras (especially neons and that ilk) love large numbers, you can 'overstock' slightly and they'll be happier than pigs in crap.
> 
> Then there are other species which merely tolerate crowding (Such as corys) where they do school, but they like their space too.
> 
> ...


I agree. My Neon Tetras always hid... untill I added 5 more, now the balance has tilted. My Glowlights have become the ones that hide, with the least number. The colors are much more vivid as well with my Neons now that i have a bit more of them as well. My Neon Rainbows and Danios tend to be happier with a few more around as well. Since they are so active, I keep fewer of them, due to size. I really watch the reaction to others to gauge how stocked I am, the behaviors change as more or less are added, as well as water chemistry as others have pointed out. There really is no set rule, but different variables that must be taken into account when stocking.


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## Super Noob (Sep 7, 2007)

An extreme of the inch not causing overcrowding would be a school of 55 chili rasboras (1") in a 55 gallon. That would be very light stocking. Throw 5 Oscars in @ 11" and you will have yourself a problem with aggression, overcrowding, and trouble keeping the water clean. I read an article on this several years ago and the only real way to have a set stocking is to go by mass. Filtration can always be increased so I don't factor that concern with this topic. A big enough filter can handle feeder fish tanks at the store.

Since size of fish isn't a factor, and neither is filtration, the only variable you can't control is how much space the fish NEED to prosper and at what level of the tank. Some fish may have a small nearly 2D space that is only along the bottom, while others may have a spacious 3D zone that cover all areas. 

Not sure if I am explaining the concept properly. If it doesn't make sense maybe someone can clear it up.


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