Poll: How Many Fish per Gallon?

dbl · Jan 31, 2018

What do you use as a guideline for your stocking density? Is it a certain number per gallon? Is it a certain number of inches of fish per gallon? Is it based on the age and bio capacity of your tank? Or do you just wing it?

It's an age old question and often asked by new members getting in to the hobby. The old Rule of Thumb is 1" of fish per gallon of water. However, the obvious answer isn't so obvious! The true answer is much more complicated and harder to understand.

So what "rule" do you use, if any?

Brian W · Jan 31, 2018

I have a general knowledge just by reading this forum. then...I ask R2R.

Breadman03 · Jan 31, 2018

It depends on the mix of species. Some of it is temperament of the species (and individual fish), the biological niche of the species, how many hiding places are available, and even how busy the tank is. Honestly, my tank has gotten more peaceful since going from 4 to 9 fish. My tank is nowhere near full, but it seems like the extra fish prevent one fish from getting singled out.

recess62 · Jan 31, 2018

I chose other. For me it is based on compatibility, size of the specimen,and bioload capacity. The number in the tank to me is not that important if the tank is able to process the waste. For example I have 15 fish and too many inverts tomcount in my 90. I have 3 “large fish “ ( Fox face, yellow tang, coral beauty). With the remainder being small wrasses blennies and clowns. All the fish seem to inhabit their own niche and has their own job in the tank. I feed heavy. There is no fighting for food. My nutrients are under control and the fish are fat and happy

CindyKz · Jan 31, 2018

I research the fish - is it appropriate in terms of tank size? Can I keep it alive and thriving? Will it get along with current tank mates? Is my bioload ok (nitrates under control, no algae problems). The hard part can be finding accurate, detailed information about the species. It's hard to know what is reliable and what is opinion.

I thought by this time I would be fully stocked (75 gal mixed reef) but my parameters are still reasonable and everyone is getting along. I keep wanting to add "just one more"

atoll · Jan 31, 2018

Fish per gallon is a myth these days, many years ago it may have applied to some extent but not today. However, fish species along with filtration employed is a more important gauge of stocking levels IMO and IME.

Crabs McJones · Jan 31, 2018

I have a general knowledge of what I can keep in my tank going based off of the recommended minimum aquarium size from sites such as liveaquaria. But if they have the fish listed i'll also use Aqua Advisor, put in my tank dimensions, and put in the fish i'm considering along with the fish I already have and it'll tell me my stocking level and recommended weekly water change amount and any hints or tips for each fish. Plus i'm never to afraid to ask the experts on r2r

S-t-r-e-t-c-h · Jan 31, 2018

1" / gallon is an old freshwater guideline that will probably get you in trouble in a full reef tank.

Have to say, I mostly wing it. Watch nitrates, know what the eventual size & temperaments are, etc. of course. But hard fast rules are neither hard nor fast in this hobby. Depending on your particular tank and equipment, you can probably maintain a higher bioload than others would.

If you put a gun to my head, I'd probably go with 1 cubic inch of fish / 10 gallons of water in a reef tank. With caveats...

recess62 · Jan 31, 2018

I totally agree with the research before you buy approach. I think one can get a reasonable idea of what to expect in a specimen by pulling together all the various resources and make an informed decision

Btw. Great thread

4FordFamily · Jan 31, 2018

Based on age, swimming room, species, nutrient export, experience, how hard you’re willing to work to keep parameters in check, and tolerance for risk

revhtree · Jan 31, 2018

I base it on the size of my tank and filtration along with the types of fish I want to keep. Also aquascaping plays a part for free swimming fish.

mort · Jan 31, 2018

Age of the tank and how effective the filtration are the most important things. Next is size of fish (biomass) and final size but diet is important as those with high protein diets put a huge strain on filtration.

Susan Edwards · Jan 31, 2018

Researching of fish size and needs in tank. I get a general guideline from the so many of A, B & C groups of fish per gallon. That way I'm sure I have all areas of tank covered and in balance. And go slow...

Tuffyyyyy · Jan 31, 2018

Anecdotally I go by 1 fish for every 10 gallons. There's a ton of variability in that as you go on but using that rule helps newbies not stuff 5 fish inside their Fulval 13.

Kremis · Jan 31, 2018

In my opinion there is no set rule for how many fish per tank size. Especially length wise. Each fish has its own individual needs. For example, frogfish. Some types of frogfish stay smaller (under 3 inches) but they generate a lot of waste and add a lot to the bioload.
I think that stocking depends on a few things:
tank dimensions
filtration
reef/noreef
what fish do you have already?

My 180 stock list is
leopard wrasse
2 clowns
2 pyramid butterflyfish
1 sand sifter goby
1 harlequin tusk
tail spot blenny
candy hogfish
royal gramma
pintail wrasse
bangai cardinal
pearly jawfish
blue tang
sailfin tang
4x lyretail anthias
lubbocks wrasse
solar fairy wrasse
In total 21 fish, and in my opinion I could add a few more smaller fish
there is very little aggresion, and my tank has heavy filtration with chaeto, socks, skimmer, GFO and weekly water changes.

saltyhog · Jan 31, 2018

Too many variables for an easy "rule". It depends on the fish's space needs, the compatibility with other fish/inverts, aquascape, maturity of the coral (large space consuming colonies may provide more hiding places for small fish but take up swimming room for active big fish). Common sense helps but I often struggle with my desire for a certain fish over riding what little common sense I have.

I really think with proper husbandry most people have more filtration than they have room for the maximum amount of fish to exist reasonably "naturally".

five.five-six · Jan 31, 2018

I voted “just wing it” but it really does depend on fish species. For instance, if you fallowed the 1” per gallon with dragonets in a 20 gallon tank you’d have real problems.

NY_Caveman · Jan 31, 2018

crabs_mcjones said:
I have a general knowledge of what I can keep in my tank going based off of the recommended minimum aquarium size from sites such as liveaquaria. But if they have the fish listed i'll also use Aqua Advisor, put in my tank dimensions, and put in the fish i'm considering along with the fish I already have and it'll tell me my stocking level and recommended weekly water change amount and any hints or tips for each fish. Plus i'm never to afraid to ask the experts on r2r

Thanks for this @crabs_mcjones. I used this site for years on freshwater planted aquariums and never even noticed they had a saltwater tab. LOL.

madweazl · Jan 31, 2018

I add fish until they start to get froggy and bicker about space.

A Toadstool Leather · Jan 31, 2018

Bioload and behavior are by far the most important imo. Some fish are more messy than others and some need more space. A 4 inch flame angel needs more space than a 4 inch clown for example.