Age Old Question: How many fish should I stock in my tank?

[Rory Waliser]

I am setting up a 29 Gallon aquarium that will be an upgraded tank for my growing bristlenose pleco. This tank will be heavily planted using eco-complete substrate and will include driftwood. I want to stock cardinal tetras in addition to my pleco, but now the question is, of course, how many. Using the inch per gallon rule that so many people say is garbage, my math comes to 12 cardinals in addition to my pleco to make the tank “100%” stocked. Using the aqadvisor calculator, a 100% stocked example comes out to 20 cardinals, my pleco, 6 cherry shrimp, and 6 nerite snails. This is obviously not using the inch per gallon scale which makes me wonder which is the better guideline. Is there enough area for a school of 20 cardinals to swim in a 29 gallon? Is that number going to create a bio load that requires 50% water changes weekly and a fortune in plant fertilizer? My worst fears are putting too many fish in and creating an unfavorable, crowded, lifestyle for the fish and putting too small of a school in and having lonely cardinals that don’t school. 

[lefty o]

with 1 pleco, a few shrimp, and a few snails, id say comfortably 20-25 cardinal tetras. with any kind of filtration, and being heavily planted, that is a conservative number.  id say a 20% water change every other week is easily feasible once the tank is cycled and established.

[Rory Waliser]

Is this a linear number just built off of available water volume per fish or does this also take into consideration the fact that they would be the only species in the tank using their preferred elevation in the water column? Like if I wanted to put 6 other fish that school and max out at about the same size as a cardinal in, would I just have then 14-19 cardinals and 6 of the others or would the number of cardinals be even less? Apologies if it’s hard to tell exactly what I’m asking. Not sure what the best way to word it is.

[Celly Rasbora]

My experience with Ember tetras has taught me that they prefer the safety of numbers. Also, my experience is that this question is often asked, but rarely definitively answered. I've heard Cory answer it with, "How often do you want to do water changes?"

[Rory Waliser]

Okay so you’re saying the more the merrier (within reason) and it’s more of a matter of how often I have to change water. That seems pretty straight forward.

[lefty o]

the real question isnt exactly how many fish per gallon, it is more of how much bio load your tank can handle without excessive maintenance, or what i really like to consider how long can the tank stay viable with a power outage where you dont have filters/air pumps, or heaters running. generally , the larger the tank, and the more plants you have the more bio load the aquarium can handle.

[Colu]

I usually go with 1in per gallon so that would be 39in of fish so you could have 25 ember tetras 2 bristles nose you can always have more if you increase filtration and do larger Water changes 

Edited February 17, 2021 by Colu
I put cardinals when I ment ember tetras

[Philip]

I'm a big fan of low and slow. Just like Barbeque. 

Start out with only one or two species, the number of each depends on how comfortable they are. So not just putting one Cory Cat in for example, rather 5 or 6. 

Then live with it for awhile. If everyone is happy and you are keeping up on the water quality, then maybe add something else. Don't go overboard, just a little.

Keep doing this until you and everyone in the tank is happy. I think people usually can tell when the balance is right. 

[gardenman]

There are roughly a gazillion variables when it comes to how many fish you can put into a tank. There is no easy answer. Throw away the inch per gallon rule as a twelve inch Oscar and twelve one-inch neon tetras produce vastly different amounts of waste. If you look at commercial aquaculture, they often stock enormous quantities of fish in relatively small tanks/ponds. The Japanese koi farmers often have insane amounts of fish crowded into their holding tanks. One joked a few years back that if you couldn't walk across a pond without getting wet there weren't enough fish in it. 

If you have a brand new tank, filter, and system it can support fewer fish than an older established tank and system. Planted tanks can hold more fish than a bare tank. Surface area matters also. Those really tall tanks have less surface area for gas exchange and can safely house fewer fish. How much you feed the fish and how often you feed them matters. Erring on the side of too few is wiser when you're starting out and as the tank gets more and more established add a few more here and there.

[Rory Waliser]

9 hours ago, Colu said:

I usually go with 1in per gallon so that would be 39in of fish so you could have 25 cardinals 2 bristles nose you can always have more if you increase filtration and do larger Water changes 

cardinals get two inches long and bristlenoses 5 inches. 25 cardinals and 2 plecos makes 60 inches in 29 gallons unless im misinterpreting something?

[Colu]

Just realized  I was think of  ember tetras  not cardinals my mistake

[Rory Waliser]

So my takeaways from this thread are:

1. Inch per gallon rule is close to worthless
2. With the amount of driftwood, my aquaclear 50, my sponge filter, my eco complete dirt, and my plants, I should have no issue with the bioload of a number of around 25 cardinals and a placo.
3. If I can still handle more bioload after my initial 25 cardinals are in, they would be even happier with a few more in the school.

Let me know if there is any holes in my logic. Thanks everyone for the input!

[TheDukeAnumber1]

Bio-load is what defines what you can put in a tank and bio-load is directly in connection with how much food you feed. You can power feed 50 tetras or lightly feed 100 tetras the same amount of food and your bio-load will be the same.

Live plants can turn the tables on bio-load by removing waste, and water changes remove waste. It all comes down to you finding a balance of feeding, plants, and water changes that works for you.

[Maggie]

The 1 inch per gallon "rule" doesn't really work for a few reasons, one of which is 1 inch of what fish? One inch of a goldfish is a lot more mass than one inch of a cardinal tetra. I have 19 rasboras and 6 otocinclus catfish in my 45, which already violates the "1 inch per gallon rule", yet all there is still room for more and enough open swimming space for them all, and they'd probably be perfectly happy if there were twice as many, though that's not what I am planning!

[starsman20]

Just now, Colu

I usually go with 1in per gallon so that would be 39in of fish so you could have 25 ember tetras 2 bristles nose you can always have more if you increase filtration and do larger Water changes 

Or 1 giant 39 inch goldfish

[Rory Waliser]

I understand why the 1 inch per gallon rule doesn't work. My original question was mainly asking why do people use it still? There seems to be no benefit to this guideline.

[Colu]

32 minutes ago, starsman20 said:

Or 1 giant 39 inch goldfish

I use 1in per gallon On smaller fish bigger fish  require a lot more filtration and room  people just have to use common sense with larger fish

[Celly Rasbora]

31 minutes ago, Rory Waliser said:

I understand why the 1 inch per gallon rule doesn't work. My original question was mainly asking why do people use it still? There seems to be no benefit to this guideline.

I don't know of any fish expert who would use this rule. I think it got started, decades ago, because the question can only be answered to fit the circumstance. I have about 40 fish in my 15 gallon, but it is heavily planted and Boraras and Ember Tetras have a small bioload. I was unprepared for how much and how big my new snails poop. But I don't mind doing water changes, and I have made a commitment to test my water more frequently.

Edited February 17, 2021 by Celly Rasbora

[Brandy]

I think this rule came to be due to employee burnout. I suspect it is simply a way to ballpark a reasonable number for people who have no intention of learning anything about the preferences of their fish.

As a bunch of fish nerds we forget that there are people out there who think of fish as decor much like a lava lamp. For these people, they are not looking to be monster fish keepers, or really even pet owners. They just want a box of animated paintchips. If you are talking to a person who just wants a comunity tank full of color that matches their livingroom "for the kids" then they want a simple, easy to remember rule. If you are working in a big box store, facing these people all day, it must get disheartening. At some point you just dial it in and give them what they want, and try to prevent the worst damage.

Edited February 17, 2021 by Brandy
quoted the wrong post! sorry!

[Rory Waliser]

34 minutes ago, Brandy said:

I think this rule came to be due to employee burnout. I suspect it is simply a way to ballpark a reasonable number for people who have no intention of learning anything about the preferences of their fish.

As a bunch of fish nerds we forget that there are people out there who think of fish as decor much like a lava lamp. For these people, they are not looking to be monster fish keepers, or really even pet owners. They just want a box of animated paintchips. If you are talking to a person who just wants a comunity tank full of color that matches their livingroom "for the kids" then they want a simple, easy to remember rule. If you are working in a big box store, facing these people all day, it must get disheartening. At some point you just dial it in and give them what they want, and try to prevent the worst damage.

This would make TOTAL sense!

[Rory Waliser]

56 minutes ago, Celly Rasbora said:

I don't know of any fish expert who would use this rule. I think it got started, decades ago, because the question can only be answered to fit the circumstance. I have about 40 fish in my 15 gallon, but it is heavily planted and Boraras and Ember Tetras have a small bioload. I was unprepared for how much and how big my new snails poop. But I don't mind doing water changes, and I have made a commitment to test my water more frequently.

Yeah I'm thinking I'm going to end up putting like 20 cardinals in it with my pleco and then add from there. I'm pretty routine with my water changes since I have 3 other smaller tanks already, so this should work just fine bioload-wise based on everybody's advice.

[Celly Rasbora]

@Rory Waliser 20 sounds like a good start. I only have 10 tetras in my tank and they are so skittish. But I'm not willing to add any more as I think I'm maxed out at the moment. I really wish I'd just kept my tank all Boraras, but I've made peace with them. Plus, I have a baby in my tank (seriously doubt it's a Rasbora), so now I'm a fish grandma! Squeee!

[CA Dad]

My 29 gallon after A LOT of research and 5 months of adding plants (healthy specimens from Aquarium Co-Op), sand, rocks and fish (after a period of quarantine)  I was given the corydoras and emerald catfish at the start. Currently, I use a hang on back filter and a large sponge filter (with an air stone inside).

Stock:

3 Corydoras aeneus (Bronze/Green Corydoras)

2 Brochis splendens (Emerald Green Catfish)

8 Paracheirodon axelrodi (Cardinal Tetras)

10 Trigonostigma hengeli (Orange Hengel Rasbora or Glowlight Harlequin)

Today, I added a pair of Trichogaster Ialius (Flame Dwarf Gourami)

7 Hemigrammus rhodostomus (Rummy Nose Tetras) that will come out of quarantine this weekend.

The fish are well balanced (among upper, middle, and lower levels of the tank), are very playful, peaceful, healthy and happy. Very pleasing to watch. 
 
I may add 4 more cardinals and 3-5 more rummy nose tetras in due time - and probably with added filtration. 

[Chiclid addict]

On 2/16/2021 at 8:04 PM, Colu said:

I usually go with 1in per gallon so that would be 39in of fish so you could have 25 ember tetras 2 bristles nose you can always have more if you increase filtration and do larger Water changes 

NO NO NO 

Inch per gallon is a terrible rule to go by this is a 7-8 inch angel fish that was kept in a to gallon tank and as you can see it had a bent dorsal fin

Edited February 24, 2021 by Angelfishlover

[b_ball34]

For me it comes down to how much food the tank consumes each day, a 5 inch Oscar eats WAY more then 5 neon tetras and in turn that food becomes waste which eventually become nitrates that you need to change out or have plants consume. Ethics also play a role, just because you change water every day so your 5 inch Oscar can survive in a 10 gal tank doesnt mean its ethical.