Let's take a new look at stocking levels

"Wow Jeremy, what an issue to blog on! I think it's been on all our minds at some point! I know it has been on mine!

I suppose there are so many factors, such as filtration, the amount of plants in the tank, (that will use up nitrates)
and of course, the maintenance routine of the keeper.

I suppose another key factor is the social well-being of the fish... For example, would a huge 'overstocked' shoal of Neon Tetras be happier socially? I suspect they would...
"

"And if they have sufficient swimming space, oxygen and food, their ammonia is being broken down and nitrate removed, is it possible to be overstocked?

Disease is a possible limiting factor in stocking, however, as many bodies in close confinement means many potential hosts."

"'Let's drag this antiquated side of the hobby into the 21st century!'
To be fair... this part of the hobby is completly with the times, its the PFK stocking calculator that isn't (see the thread i posted on the forum complaining for full details lol)
;)"

"My thoughts for the maximum stocking guide of an 'average' planted freshwater tank with regular maintenance and good plant growth, CO2 turned off at night -

1-2cm of small fish per litre.

Towards 1cm/litre for lower-growth set-ups, 2cm/litre for higher-growth setups."

"Talking rule of thumb, and for average non carnivore big guys (like triggers, puffer, and lionfis) then for a reef i would say about 1cm for every 4-5 litre, at the very most for well filtered system. And for a fish only 1cm for every 3 litres, is the probable max.
Cant possibly comment on freshy's my self, as i dont and never have kept them.
But of course it depends on filtration."

"I agree, I have a 125l tank-27 gallons.
In which I have 35kilos of rock, 8 pounds of gravel, and a weir. That probably takes up 4 gallons, which leaves 23 gall for fish, or going by the inch per gall rule 23 inches of fish.

The tank is a Mbuna set-up in which I have 17 fish that are around 3 or 4 inches long. Call it 3.5 and that is about 60 inches! Or nearly 3 times the reccomended level.

Yet my fish are happy and healthy, I use a powerhead which pulls 1500l an hour through the filter, so that's about 15x turnover.

I think stocking levels should take level of filtration and type of fish into account.

I agree the inch per gall 'rule' is at best unhelpful.

Karl
"

"Im one that is guilty of 'overstocking'.
I would personally go for less than what George says as that would equate to 80+ ember tetras in a 60l tank which i think would be pushing it.
I think it also depends on eating habits and body mass of said fish.
You could squash a few hundred neon tetras into the space of a single oscar, and they would also quite hapily live off flake and live food as aposed to higher puluting foods.
"

"i think that stocking level guidelines need a good looking at as i had a 48"x15"x18" tropical tank containing two tiger oscars, three banded leporenus, a 20"+ common plec and a bircher running an external filter. Water was tested weekly and never had any readings above the reccomended maximum.
i am now keeping marines and am slowly stocking the tank with more than the recomended toal maximum length of fish so i can keep an eye on water parameters.
and so far things are 100% perfect apart from unwanted algae that refuses to go despite all the phosphate remover added to the filtration system!!!!
lets hope you can come up with a more sensible fish stocking system!!
I remember jeremy working at an aquatic retailer in northampton telling me the maximum of fish i could keep and my tank looked very empty..
"

"To do this justice, you need to be scientific about it. There are so many variables involved that just taking stabs or trying out different set ups randomly isn't going to help move it forward. The article by Jay Hemdal in the July issue was a start, but it still needs more work and needs to incorporate some of the other factors like filtration etc that are currently missing. I think that to get to anything that is meaningful will take a massive empirical and scientific study, which I can't see being funded anytime soon I'm sad to say."

"Commercial fish farming industry calculations are based on fish weight, weight of food fed, protein content of food, and oxygen levels. "

" There is no simple equation for stocking levels. There are too many variables, including the species kept, the amount of maintenance done, and even the temperature of the tank.

One factor which is not usually considered but vitally important is the size of the fish.

When stocking a tank, most people assume that -

24x1"fish = 12x2"fish = 6x4"fish and so on.......

However, a 2" fish is actually the equivalent of EIGHT 1"fish, and a 4" fish is equivalent to EIGHT 2" fish.

This is basic mathematics. Think of a 1" cube. Now double the length and keep the same shape, and you get a 2" cube. This contains 8x 1"cubes. This law works for all shapes.
When a fish doubles it's length it generally stays the same shape, therefore it becomes 8 times as big. This means 8 times the Oxygen intake and CO2 output, 8 times the food, 8 times the waste and therefore 8 times the filtration required.

So an 8" Oscar is the equivalent of 512x1" Oscars. If it was hollow you could actually fit 512 of them inside it. I know its hard to believe but it's true.

Now I'm not suggesting that anyone should keep 2000x 1" fish in a tank that will happily hold 4x 8" fish, because other factors come into play,such as varying needs for personal space, 'peace and quiet', swimming room, etc. Because of these factors, a mixed community of several different species and types of fish requires a much lower stocking density. But small shoaling species such as Neons and other tetras, danios, etc, which actually LIKE crowds, are perfectly happy at the high stocking densities which we often see in shops.

Stocking levels are anything but rigid. It all depends on many, many factors - the size of the fish, the species, the other inhabitants, and of course the suitability of the tank maintenance. The more highly stocked the tank is, the more water changes are required (more water changed, and more often, which is perfectly fine if the incoming water is of good quality and very similar in composition. Fish never object to large water changes with good, appropriate water. They just object to changes in the composition.)

The more I'm getting into this, the more I'm realising that it's getting no nearer to an answer. That's because there isnt one. There are too many factors involved for there to be a simple equation for stocking levels. Its really a case of seeking advice as a beginner for the fish they are keeping (there are many internet forums where experienced, conscientious aquarists will happily help), and then learning by experience."

"I don't think stocking level calculators are of any value. The best guide is the amount of maintenance needed. If you spend all your time cleaning filters and scraping algae then you've too many fish.

An other thing to consider is that although filters etc. may allow us to keep more fish in a given volume, they can and do fail. I always understock my tanks so that I have a safety margin in the event of equipment malfunction."

"Carl just by way of recommendation I would suggest a number of mithrax crabs to tackle the algae especially if it is hair algae, I added 5 to my 55 gallon reef and in combination with a large number of partial water changes I have fixed the problem. I also found that the only phosphate remover that really helped was rowaphos no idea why it just seems to do the job better than anything else.

Back to topic stocking levels are difficult even on a freshwater system ideally you would want to do any calculation on the basis of biomass! Not an easy task how many people weigh their fish and would a neon even register on conventional scales?

I think things need to be worked out on a combination of total water volume flow rate and aeration/surface agitation. I think one of the major limiting factors with freshwater tanks is gas exchange and is the rate of gas exchange quicker than the rate of depletion by the number of fish.

Also there is the welfare angle how much space does a fish need, is it solitary or social is it nocturnal. Then of course there are the predation concerns and with that dietary requirements.

I probably would be accused of over stocking on one of my tanks it is a 100 gallon tank 4x2x2 and contains I have about 40 fish in the tank the smallest about 2" the largest 12" the average fish size is about 6" so a total of 240" of fish in total.

The tank could comfortably accomadate 300 plus cardinals yet is 240" of african catfish and medium sized cichlids and large tetras of concern.

According to conventional guidelines I could keep 300" of community fish where as I have a community tank but it is a large fish community, I know full well that it would take in excess of 1,000 cardinals to produce even half the waste my current fish produce.

I think any calculation for freshwater has to take in to account at the very least the average fish size, total water volume, flow rate through the filters, plus the surface area of the filter media. With out this any guide is no better than a guess.

Reef tanks are a different matter I think it is important to keep the stocking levels low due to the territorial habits of reef fish as well as the risks of disease and unwanted algae. However some fish can be considered an exception to this rule such as shoaling species that do not hold territories such as green chromis or cardinal fish or other such species. The food used is also of concern I use to feed frozen food I have now changed to flake food this means I can feed more often and I don't have the result of putting unwanted pollutants into the tank.

Anyway the below are the general rules I follow:

Freshwater - Always over rate the filters and use media with the highest possible surface area to maximise bacterial volume, my 4x2x2 has 3 filters 1 fluidised sand filter rated to a tank upto 150 gallons 1 eheim 2250 filled with ehfi substrat (9 litres of it) and an old fluval 303 full of filter wool to polish the water, large fish produce a lot of particulates! I then establish what the max tank size I could run on the filters, the filter I use could run a tank up to 400 gallons. I have presumed that their guidelines are based on said out of date stocking density guidelines so I use this as my upper limit, I will add that I will never stock to this upper limit, I then look at the max guidelines for the tank size and then I make a reasonable judgement based on my experience of fish keeping and what I hope to stock.

Marine - This is a completely different ball game you would need to consider the various reef set up types berlin or eco system then you have the combo systemsthen the DIY designed systems like mine which uses bits of the eco method and the berlin there are just to many variables generally speaking I would say it really depends on the diet of the fish to be kept predators would pollute more so take up more stocking points than a herbivorous fish does, then you have to factor in the janitors too!

It is a challenging objective refining these guidelines and it is difficult to know where to start."

"I think Mark Wright's comments on fish volume comparisons is way off the mark (pardon the pun). Fish aren't cubes therefore this mathematical law does not apply. Fish come in all sorts of shapes and volumes. An 8" Khuli loach won't have anywhere near the same body volume as an 8" Oscar. But I agree with Mark's other comments on the complexities of arriving at a stocking level formula. There are just too many variables. As a scientist I think the only answer is for aquarists to be guided by their water parameters and fish behaviour.

Regards,

Gordon Turner"

"There seems to be many good valid points about stocking in the comments. However in the guidelines in my opinion it would be better to be on the safe side as the people who most need these guidelines are usually people new to fish keeping who just need safe simple rules, not the kind " depending on your filtration system and water change regime..." When experience grows thats when you can (hopefully!) see yourself whether you can stock your tank more."

"Personaly, I do some research about the fish I want to keep, look at there habits, fast swimmer, lively or a slow mover, just hanging around.Most important, what is the volume of water that they need to breed in (surface and depth.
Divide you aquarium into 3 layers: bottom, middle and surface, repeat those calculation for each layer.
If you take a shoal of fish, try to estimate the volume of that shoal and use those dimensions as if they where one fish.
Whit al these data you can make an estimate about the volume of water that they each need to be happy. "

"These days, getting a decent nitrifying bacteria colony is very easy using modern technology.

We know that the surface area of the filtering media is very important and we can use advanced media with twenty times the area of a piece of sponge or glass balls.

So effectively allowing more fish than 'usual' to be put in a given space and still removing the nitrogen toxins.

But the overriding factor for stocking is still oxygen levels. Bacteria and fish need oxygen and so far we don't usually dump this artificially in, so the gas exchange area of the water surface is still the main stocking factor surely?

Plants obviously supply O2 during the day, but at night they don't so again the water surface needs to be able to support the population at night.

Unless some clever Scientist finds a strain of bacteria that eats fish waste and produces oxygen 24hours. Could happen I suppose... ;-)
"

"less is more folks"

"I think there are too many variables for any system to come up with a hard n fast 'catch all' rule.

So - my advise to those publishing advise is this - how about giving guidance to the newcomers that will enable them to have a healthy and relatively trouble free system to begin with.

Common sense tells the average fishkeeper whether the stocking is too high etc (which comes from experience) and as mentioned - factors such as the species of fish, flitration, planting etc etc etc etc etc etc etc etc etct all have an impact on the levels.

One could argue 'as long as I get zero nitrite an ammonia in my fresh tropical tank - stock levels dont matter' but what about 'personal space' for fish - call it comfort level.

This business of 'x inches per x liters' etc is rowlocks - is having (for example) 30 neons at 1inch each the same as a 30inch plec ? no it isnt but the current stocking guides give this illusion.

I actually think an entire book could be written on stocking levels alone - I'm no expert on fish keeping - Ive only been at it for some 30months - I know my tank is theoretically 'overstocked' but the system runs fine and the tankmates are fine (and happily breeding - isn't that a key indicator of health and happiness?)

Ive been on several fishkeeping forums and am tired of the tirades some people dish out about overstocking (im not talking about big fish in small tanks here) - these people are obviously basing their 'knowledge' on old and outdated methods.

My advice if anyone asks me what I think of their levels is to ask them what filtration etc etc etc etc they currently have.

Buying a system from a shop (tank filter etc) is where most folk start - now I know that I couldn't keep my stock in the tank I have - if I hadn't added filters (and upgraded etc) over time.

You may not like me doing this but the thinkfish website has a stock calculator which I believe is reasonably accurate - at the end of the day - no two tanks are the same."

"I think Mark & Alan's comments are very interesting & true that there is no hard & fast rules for anything-too many variables, all we can do is use judgement & common sense & shared knowledge from the experts. I believe the most important factor to keeping a happy, healthy tank is frequent & large water changes-I have 5 Common/Comet Goldfish all approx 5-6 inches long in an 8 foot 100 gallon long tank run by a 35 gallon sump which turns the tank over about 10 times per hour. I do 2 x 33% water changes per week & my NO3 is around 10. I reckon if I did twice the amount of water changes or changed out twice the volume each time I could keep maybe twice as many fish in the tank while keeping the water quality identical. However, my concerns over this would be twofold-firstly the fish are constantly growing, taking up more room & secondly they may feel like they are overcrowded with the resulting outbreak of Ich etc & I like to keep my fish happy!

I am a member of a forum that runs from beginner to expert & from my experience on there I would say that the current simplistic stocking calculators we have are difficult enough for beginners to grasp so upgrading them to include several vaiables would almost certainly cloud the water further for them in an already mind-boggling sea of options. "

"One little point I would like to make on this stocking level front is, not only do we need to consider type of fish size, etc, maturation of filter but also aquatic knowledge / experience of the keeper.

An experienced fish keeper can keep an "overstocked" tank healthy far easier than a beginner.

"