Backyard Aquaponics
A place to discuss aquaponics

I don't recall ever seeing an answer to this.

Nothing I've read indicates the bacteria struggle to find the ammonia and nitrites when they are dilute, but not knowing isn't really an answer.

I doubt your fish would care either way.

I have read of EB commiserating about the 2:1 ratio on this forum, So is the 2:1 ratio a total croc?
I want the best results for my plants and fish. If my plants would benefit from being closer to the 2:1 ratio I would pursue that line more keenly. At the moment I dont believe they (plants) are living up to AP potential that I have seen on this forum.
If being closer to the 2:1 ratio is of no advantage to plants I will fill tank back up to its max level so that the fish have more room to live in.

Or is the formula more like,
kg of fish in FT : GB volume, if so what would be the optimum or recomended ratio of this ?

It's more a max of 30kg/1000L of fish tank volume: growbed volume...

The "norm" in FT:Growbed volume seems to have become 1:1.... but really, as the grow bed volume is our filtration volume.... and filtration requires a capacity to match maximum feed rates...

IMO.. a 1:1 ratio is boderline in terms of filtration... and the old 1:2 ratio of tank volume : growbed volume... is a safer recommendation....

In the BYAP handbook I have, it suggests a stocking density of 6kg / 100lt of FT. Thats is double the stocking density that your suggesting Rupe. Unless my math is wrong.
With the fish I have in my system if I grow them out to 750gm it will give me a Fish kg total of about 30kg, equating to 500lt FT to run them comfortably. My issue is that the min I can run my FT is about 940 lt. So by my calc I need to almost double my fish numbers to get to the 6kg / 100 lt stocking density.
If I go by your recomendation 30 kg / 1000 lt. FT, Rupe then I am stocking at about the right amount. I will still need to add more GB as at the moment I have only 990 lt. GB.

[quote="skipd"]In the BYAP handbook I have, it suggests a stocking density of 6kg / 100lt of FT.
This handbook is probably about 5 years old.

skipd, don't get so hung up on the 2 growbed : 1 fish tank volume ratio. Many recommendations have surfaced over the years and really it is a recommendation based on the experiences of others have come before you, I and some others on the forum... It is not as concrete as a mathematical or scientific formula...

Most recently, BYAP forum tries to recommend people stock their system to 20-25 fishes per 500L of growbed (filtration) volume (based on average 500-600gms per fish). I would personally suggest that you still to these guidelines.

If you take a step back and analyse the 2:1 growbed to fish tank volume, the 3kg/100 lt and 20-25 fishes per 500L of growbed, it is all centred around an important parameter. Filtration.

So I guess you are hung up about you not getting a 2:1 ratio with your system, but I think your system will meet the 20-25 fishes per 500L of growbed guideline... so stick with that... 2:1 is better filtration but are you currently experiencing a filtration problem (ie.. high ammonia and nitrites)??

You need to look at all the recommendations for AP together, not in isolation like what you have done.

I would suggest you top your tank up to its full capacity (over a few days of course) because more water mass gives better temperature stability, hence better fish health. And this is what I am referring to about looking at AP as a complete compromising natural system rather than homing down on each recommendation and make each one of them fit the box.

Cheers Ivan,
Well no I dont have issues with ammonia or nitrites.
So it is as I thought it might be a fish KG / GB volume that matters.
As luck would have it then my Fish stocking / GB is about right.
I guess I just dont get the theory of fill the tank to its capacity, Are you saying that the FT volume could be 2000lt or 5000lt and does not matter or are you actually aware from my previous posts that my FT capacity is 1700 lt.

And it's currently being revised into a new edition.... I also used to recommend Ebara optima pumps back then..

Yeah like Ivan suggests..
Definitely fill your tank up, keep your fish as happy as possible with as much water as possible..

skipd, yes I was aware that your tank size is 1700lt and I believe it should be alright up to 5000lt. You will generally find that if someone has a 5000lt tank, he will intend to add more growbeds later anyways...

Sure this go against the 2:1 growbed to fish tank ratio, but if you get what I am trying to explain. It is about how much filtration you have to how many fish you can keep. The problem with most people starting out in this hobby, is that they are results-driven and normally ask "How many fishes you can keep in that tank?" Very seldom you get someone ask "How filtration I need to keep x fishes?" So in order to relate the number of fish to the tank size then to the filtration, I believe that is how the 2:1 ratio came about.

But skip all that... Just focus on the important parameter that all this ratios are targeted toward... Filtration... But of coz you still need to remember that you will still need enough water left in the tank for the fishes to swim in...

Sorry but filling up my FT goes against the stocking parameters mentioned by Ivan.
If I go by Ivans observation, 3kg fish / 100lt FT & 20-25 (5-600gm) fishes / 500lt GB. this is how my system should measure.
For ease of calculating I will set my FT at 1000lt therefore 30kg of fish (I will need to get another 10 fish) and
My current GBs hold 990lt (could easily top them up to reach 1000lt) so I will calculate this at 1000 lt as well, therefore 40-50 fishes (I currently have about 40, not including the 7 goldfish).
If the 3kg of fish / 100lt is guide I am nowhere near that currently, even if I am running my FT at its lowest possible level of about 940 lt.as my average fish size is about 100g (caught one today to weigh).
So why would I want to fill up my FT to its capacity of 1700 lt when I have just been advised of the fish kg/ FT stocking rate.
I know I am banging on and if I have missed something then I am a d...head.
I want to run the system to its optimum, if not then I figure its a bit of a waste of time, and to run the system at its peak then I feel I need to have every part of the system working at its optimum level.

Hi Ivan, just saw your post and tried to edit mine.
I hear you re. fish swimming and I am not really trying to cram as many fish in as possable just to run waht I have got to the best of its ability.
Ultimately I am sure that the 2:1 ratio would be best as you can have GBs at different stages of growth and still get good filtration and plant using nitrate capacity.

Anyone , thoughts

I went on to say in subsequent post that I thought ultimately I am striving for 2:1 ratio as this would handy for rotating crops and allowing for GBs to be at different growth stages and still getting good Nitrate usage.

I dont want to stock nesecarily to capacity but want my system to be the best it can be at this stage and as it grows.

I appreciate the ideas and advice and hope you have all had a great weekend
Regards, Skipd.

Quite simply... you can't have too much filtration... but you can have too many fish...

Your posts seem to be a lot like mine when I was first on the forum.

First of all the 2:1 guideline (not rule) was first proposed by the Spreaneos (sp). It is more correctly stated as :

1kg of fish : 16.67L of FT : 33.33L of gravel based filter : 0.11m2 of growing area for tilapia and a mix of fruiting and leafy green vegies.

2:1 is much easier to say but you need to understand the parameters on which it was based. First of all they were growing tilapia at densities of around 60kg/1000L. Second the filter was the gravel beds which were 30cm deep.

The Spraneos work was obviously with their design and the conditions they had to deal with. Change their design, crops, species etc. and their well researched rule is just a guideline, a starting point from which we can begin.

The uvi system has different ratios but their system is very different. Principally because they removed solids.