Backyard Aquaponics
A place to discuss aquaponics

One of the major discords between myself and a well known "aquaponics guru".. that resulted both in a previous banning, and the recent banning from the same forum...

Is the question of stocking density... and the often quoted... or misinterpreted "1 fish in 10L of water" suggestion...

I've fully acknowledgeed that the author of the "infamous" suggestion... does "qualify" the suggestion elsewhere in his blogs...

(Although some of the suggested cavaets are as unfounded as the principle suggestion in question)

But I've repeatedly pointed out that many people just aren't aware of the "caveats" that he attaches...

And just blissfully accept the suggestion of "1 fish per 10L"... in itself.... very probably because of the authors "standing" in the aquaponics community...

And on that basis, even pleaded with him.... to once and for all... to remove the suggestion from any of his materials... and refrain from making it further.... sadly to no avail... and indeed the same suggestion was actually "asserted" in a recent post...

The response, sometimes publically, but more often privately.... was usually just.... that I was "making it up"....

Yet here again.. and there are many occasions when it arises... is a poster experienceing problems, or raising concerns.. partly due to stocking to that level....



A new "uncycled" 1000L system... with about 400L (max) of grow bed filtration... (and a small raft)....

Stocked with 100 x 70mm fish.... and an obviously new, and inexperienced user... worried about levels....

One of the "caveats" often trotted out in support of the "1 fish per 10L" suggestion... is the fish are "only small"....

Perhaps suggesting therefore... that, thus they wont cause any problems, or concerns...

Well, yes... in this case part of the problem is the fact that the user is inexperienced, and the system is "cycling".... and indeed the levels are not excessively high....

But stocked appropriately... with good guidance as to cycling with fish... the user wouldn't have reason to be concerned at all with his readings..

The real concern though... is once cycled... and consistant feeding begins... and increases over time... the user will undoubtably experience problems in the future....

And well before the suggested ..."unevenly" growing fish... get anywhere near the suggested "start eating them" stage...

Because the system has been overstocked.... to the infamous "1 fish per 10L" suggestion...

Without regard to, or with any understanding of what would actually be required to main such a level of stocking density...

And the "cavaets" sometimes attached to qualify the suggestion... just don't, and won't cut it... at that level of density.... regardless...

So is the issue with the stocking density suggestion of 1 fish per 10 liters or with the fact that newbies aren't getting the proper info to utilize that rule of thumb?

I'm about to stock my tank. I have a 100-120 gallon tank with just over 60 gallons of grow bed space. I had intended to throw in 25 fingerlings, which would put the density at about 1 fish per 10L of grow bed space and up to 1 fish per 15-20 liters of fish tank. I had assumed that this would be adequate since I am doing a fishless cycle. I am anticipating probably having to put in aeration beyond the normal splashy kind, and would probably do that regardless (don't like having a single point of failure that can cause fish armageddon.)

i'd go with half that many fish slowrider..
25lbs grown out size for every 100 gallons of gb is pretty good starting point

IMO the whole 1fish per 10L is a maximum stocking density for your water constantly in the FT(below your tide level) provided you have adequate filtration

Well that's certainly partly the problem Slowrider....

But "1 fish per 10L" is just not a stocking density to suggest for a new system... and/or a new inexperienced user....

And just not sustainable any way in a backyard system.... unless it's designed within aquaculture principles.. and with aquacultural knowledge....

Both from a filtration and oxygenation perspective.... 100 x 400-500gm fish (the suggested eating size).. is equivalent to a stocking density of 40-50kg/m3....

And that's a relatively high density, high management system in an aquacultural RAS operation...

One which would be designed with large solids removal, filtration... and high volume aeration....


I've recently seen the suggestion of "1 fish per 10L of grow bed"... being hawked around the US forums...

While it's "better"... and certainly correct to equate density to available filtration....i.e. your grow bed capacity.... (forget equating it to your tank volume altogether)....

It's still too high for most fish in backyard systems.... (Note : Tilapia are a much more forgiving fish than most others)

The normal suggested density would be half that... or to put it the way it is normally expressed.. about 1 fish per 20-25L of grow bed....

In your case about 12-15 fish maximum...

In a new system, we often suggest even starting with less than that...


It really doesn't matter whether you're fishless cycling... or cycling with fish.... as far as stocking density is concerned...

Although stocking lower (certainly if cycling with fish).... gives a greater margin for error, and time to respond... and more fish can be introduced later as the system and bacteria mature...

Filtration is only one part of it though Freebz... certainly a major part...

But the often forgotten part of the equation.... is the oxygen requirement... for fish respiration, flesh production, waste conversion....

All eventually.. and entirely... related to feed rate..... (and number of fish - part of the determiend feed rate)....

A backyard system at the suggested stocking density.... without external oxygenation.... just wont cut it at the height of summer... with fish feeding at maximum... and nearing harvest/plate size...

It's a system on the edge of disaster....

Even if you look at Wilson Lennards sizing tool.. you'll see a maximum stocking density.. for a media bed system... of around 17kg/m3....

That's 34-35 x 400-500gm fish... maximum....

It's just a push for people to forge their own aquaponic identity, and hey if you can magically double the amount of fish someone else says, you sound more impressive...

Our systems must be pretty crap if they only grow half the fish of someone else's systems/plans...

... aint that the truth...

And there's been an aweful lot of "re-invention"... and identity forging lately....

Which guru are we talking about the fish killer or the schizophrenic?

At those levels 40-50kgm3 you would also need an expensive control system. I think the generally excepted level on this forum is around 20kg/m3. Which would be 1 fish/25L of FT and 1 fish/50L of GB (based on the 2:1 rule).

I don't understand how this guy in particular and others who do the same thing can expect to have a good rep other than in the short term. The more widely they are followed the bigger the stink that will eventually come about from their advice. What standing will they have when so many people will have dead fish.

The "guru" assures me that the problem "doesn't exist"... and that as far as reported fish deaths are concerned... I'm "making it up" Stuart...

Despite the fact that many people... including Wilson Lennard... many of the aquaculture members... and others.... consistantly advise stocking around 20-25kg/m3 maximum...

yeah I read that Rup, thought the same, that PH at that level would make that ammonia pretty toxic, nevermind the nitrite reading which would also go up once that ammonia has been converted.

I did try and post on there once before saying that going by his suggestion I would be able to fit 100 trout in my 1000l tank but no way would I do it, I was actually disagreeing with him and agreeing with you but I dont think he took it that way.

The problem with caveats is ppl dont read them, or they have to take so much in that they forgot or miss it.. I read a LOT of info before I got my systems and still read stuff every day on here and other sites like Murrays(mostly these two) but I would have to say that of the two sites this one is more conservative on stocking density which me having newer systems to me is FAR more advisable. It is pretty obvious to me that if I had stocked 100 trout instead of the 45 I would of ran into issues here, I may increase my stocking level in the future once it fully matures and I get more of a handle on planting out in time etc so I can really maximise the amount of growing I get, but for the time being I am going to take it easy.(or get more fishtank hehe)

IMO the stocking should be KG of fish per x amount of grow bed material rather then fish per volume of water. Or to expand further KG of fish per GB volume with a max of 1 fish per 10L in that calculation. Maybe an online calculator that would give you a stocking indicator would be handy???

There are online calculators... search for Wilson Lennards sizing tool... for instance...

I was thinking on this site mate

On this site... it's commonly, and consistantly... suggested as a maximum of... 1 fish per 20L of grow bed capacity...

The fish tank volume has nothing to do with the equation... (within reason... i.e really small tanks)...

Forget the "1 fish per 10L" of water stuff.... min, max... or otherwise.... it just gets siezed upon... without qualification....

And even with some of the suggested qualifications.... it's just potentially dangerous...

I think I now know. He does seem to live in a different world.