How to calculate fish ratio on a system

Vonapster

Hi all,
I’ve read many different views and methods about this topic and I’m interested on peoples experience working out the ratios theoretically and practically!

Is it best practice to start off with the total size of your grow beds as the constant value and from there start the ratio sequence?

Total grow bed size (Square area or volume) determines the amount of fish required which will in turn give you the required water volume for your fish tank.

Can you also work out the same values by knowing the water volume of your fish tank as the constant......

Water volume of fish tank determines amount of fish required which will in turn give you the total grow bed size (Square area or volume).

I’m sure there are a lot of variables including species of fish, how big (by weight) your fish grow before harvest time (i.e. 500g or 1 kg) and maybe material used in growbeds.

Look forward to your comments

Dangerous Dave

I think most of the experienced people on here will tell you that the most important ratio is the volume of wet media in your system to fish - assuming no extra biological filtration. But I suppose you can start with any one of the variable and work it out.

Have a look at viewtopic.php?f=18&t=28865&p=556015&hilit=rules+of+thumb#p556015 if you haven't already.

I started out with slightly more fish (silver perch) per volume of wet media than the suggested 500 gram at adult size per 20 L. Aquaponics systems are fairly forgiving in respect of most of the ratios - and maybe I was lucky. But I've had to squeeze a lot of plants and an extra growbed in to my system as the fish got bigger... and still have off the chart nitrate readings (some say that's a bad thing but I eat plenty of salad and the occasional fish).

Mr Damage

Most people start with the known/intended square meterage of the GB's and work from there, usually because they are either limited by space, or only require a certain amount of veggies.

Starting with the GB area and working back from there to figure out how many fish will be required to produce healthy plants, and what FT volume would be required, is probably the most sensible option in those cases.

Simple version:

- Build your gravel filled GB's so that they can hold the widely recommended 300mm total gravel depth.

- Make the max flooded level in the GB's about 40-50mm from the surface.

- Figure out the total wet gravel volume.

- Match total wet gravel volume with FT water volume at 1:1 ratio, or close to ideally. This is fairly flexible, can be as high as 2:1, or as low as 0.5:1 (most chop and flip IBC systems) and still work effectively.

- Stock system with fish at 1x fish per 20L of wet gravel for slow growers, ie: Silver Perch... or 25L per fish for fast growers such as Trout, Barra etc. These ratios are based on a maximum grow out size of around 500gm.

- This will give a fairly balanced system and reasonable concentration of nutrient in the water for most commonly grown veggies.

If not limited for space, you could start with the FT water volume (ie: if you already have a tank available) and work backwards, as long as those ratios are fairly closely adhered to.

GurkanYeniceri

Would Dr Lennard's fact sheet help?

All of his fact sheets are here too.

Vonapster

MD you quoted....

Match total wet gravel volume with FT water volume at 1:1 ratio, or close to ideally. This is fairly flexible, can be as high as 2:1, or as low as 0.5:1 (most chop and flip IBC systems) and still work effectively.

So if I calculated that I have 1000 litres Total wet gravel volume and using the 1:1 ratio I would need a 1000 litre Fish tank.

If I used the 2:1 ratio then I could get away with a 500 litre Fish tank and with the 0.5:1 ratio you would have a generous 1500 litre Fish tank......Is that correct?

With the 2:1 ratio systems, do they require a sump tank to ensure constant volume in the Fish tank?
Alternatively can you alternate the flood and drain sequence so they drain at different intervals to the grow beds to eliminate the use of a sump tank?

Since I’ve mentioned a sump tank, I’m curious on how they work and why?
Is the Sump tank usually located or installed to receive the water from multiple growbeds when they drain?
Do you need a second smaller pump in the sump tank and if so what triggers the pump to run and what stops it from running so the pump doesn’t dry out the sump tank? I.E. Use of a float switch or is there a less complicated way?

Thanks again Mr Damage, Dangerous Dave and Gurkan for your comments and advice :notworthy:

danny

yeah one of the main advantages of sump tanks is to keep a constant water level in fish tank in flood and drain systems. They can also be helpful in minimizing temp fluctuations. A pretty standard well functioning design is to have a fish tank with SLO to grow beds (this removes settled solids from FT), then grow beds drain perhaps via bell siphons into sump tank, and from there water is pumped back up to FT. In these systems you get solid waste in grow beds, which some people like as it provides a fuller nutrient spectrum to plants, they also have worm colonies in grow beds to help mineralize the waste, and also a good additional source of food for fish.

The fact that the FT has to be higher up than GBs in this design can be an issue for some people so they have components ordered differently, there are many many possibilities, but everyone wants to remove solid waste from the FT and keep its water level relatively constant. In conventional designs the use of 2 pumps is never necessary or recommendable, pump from lowest to highest point and gravity does the rest.

Dangerous Dave

Thumbs up to danny's advice on sump tanks and avoiding two pumps.

Not sure what you mean about alternating a flood and drain sequence... but I imagine it's just about impossible to get two bell syphons to stay in sync and, even if doing it with some sort of timer on your pump, it would be unnecessarily complicating things.

You can have constant height in your fish tank without a sump tank if your growbed is constant flood. There are numerous debates/discussions on here about the relative merits of constant flood beds versus beds draining with a bell syphon. I have one of each and both work well.

Vonapster wrote:

If I used the 2:1 ratio then I could get away with a 500 litre Fish tank and with the 0.5:1 ratio you would have a generous 1500 litre Fish tank......Is that correct?

I think the 0.5:1 ratio has a 2000 L tank. But the key issue is that there is a wide range of ratios that will work. By contrast, the fish to wet media ratio can be less forgiving - if you do what I did and order too many fish

Vonapster

danny wrote:

A pretty standard well functioning design is to have a fish tank with SLO to grow beds (this removes settled solids from FT), then grow beds drain perhaps via bell siphons into sump tank, and from there water is pumped back up to FT. In these systems you get solid waste in grow beds, which some people like as it provides a fuller nutrient spectrum to plants, they also have worm colonies in grow beds to help mineralize the waste, and also a good additional source of food for the fish

Forgive me about my query but when you refer to”SLO” what does that abbreviation mean?

Also how does solid waste get into the grow beds if the “SLO” component is removing the solids from the fish tank before water is entering the grow beds?

Can you still get solids into the sump tank while the water is draining from the grow beds?

Dangerous Dave wrote:

Thumbs up to danny's advice on sump tanks and avoiding two pumps.

Not sure what you mean about alternating a flood and drain sequence... but I imagine it's just about impossible to get two bell syphons to stay in sync....

I didn’t explain myself quite well but what I was meaning to say is that you flood and drain grow bed 1 without the possibility of grow beds 2 and 3 to flood and drain, once grow bed 1 has finished then grow bed 2 starts its sequence, locking out the ability for GB 1 & 3 to flood and drain.
Maybe this is possible via timers and relays but not very cost effective and high risk off system failure etc.

Vonapster wrote:

If I used the 2:1 ratio then I could get away with a 500 litre Fish tank and with the 0.5:1 ratio you would have a generous 1500 litre Fish tank......Is that correct?

Dangerous Dave wrote:

I think the 0.5:1 ratio has a 2000 L tank. But the key issue is that there is a wide range of ratios that will work. By contrast, the fish to wet media ratio can be less forgiving - if you do what I did and order too many fish

Yep your right it is 2000 litres

Thanks guys

Dangerous Dave

Vonapster wrote:

danny wrote:

A pretty standard well functioning design is to have a fish tank with SLO to grow beds (this removes settled solids from FT), then grow beds drain perhaps via bell siphons into sump tank, and from there water is pumped back up to FT. In these systems you get solid waste in grow beds, which some people like as it provides a fuller nutrient spectrum to plants, they also have worm colonies in grow beds to help mineralize the waste, and also a good additional source of food for the fish

Forgive me about my query but when you refer to”SLO” what does that abbreviation mean?

Also how does solid waste get into the grow beds if the “SLO” component is removing the solids from the fish tank before water is entering the grow beds?
Could solids possibly get into the sump tank when draining from the grow beds?

Dangerous Dave wrote:

Thumbs up to danny's advice on sump tanks and avoiding two pumps.

Not sure what you mean about alternating a flood and drain sequence... but I imagine it's just about impossible to get two bell syphons to stay in sync....

I didn’t explain myself quite well but what I was meaning to say is that you flood and drain grow bed 1 without the possibility of grow beds 2 and 3 to drflood and drain, once grow bed 1 has finished then grow bed 2 starts its sequence, locking out the ability for GB 1 & 3 to flood and drain.
Maybe this is possible via timers and relays but not very cost effective and high risk off system failure etc.

Vonapster wrote:

If I used the 2:1 ratio then I could get away with a 500 litre Fish tank and with the 0.5:1 ratio you would have a generous 1500 litre Fish tank......Is that correct?

Dangerous Dave wrote:

I think the 0.5:1 ratio has a 2000 L tank. But the key issue is that there is a wide range of ratios that will work. By contrast, the fish to wet media ratio can be less forgiving - if you do what I did and order too many fish

Yep your right it is 2000 litres

Thanks guys

Solids lift overflow removes FT solids to wherever the outflow pipe runs... Most likely growbed.

Sent from my Pixel using Tapatalk

danny

This is the basic principle... its just an overflow outlet but the inlet is at the bottom in order to draw in the settled solid waste. In reality they are a little different in design to optimise solid intake and to avoid unwanted siphoning action.

Vonapster

Thanks for that simple diagram.

So my understanding for it to work is that the FT water level is always above the outlet pipe level and works by gravity.
Keeping the FT water level constant is achieved by having a sump tank in the system. Could you explain the relationship between the two? How is this achieved?

Sorry if my questions are basic knowledge but I’m interested to learn about the different components used in aquaponics, how they operate, why they are used and what the pros and cons are?
I’m like a dry sponge void of water ha ha
I want to build a large system in the future so I’m getting as much knowledge and information as possible!

Mr Damage

Vonapster wrote:

So my understanding for it to work is that the FT water level is always above the outlet pipe level and works by gravity.!

Not above the oultet pipe, level with, see the diagram below. The SLO's vertical has a 'T' piece on top to stop it turning into a siphon, as Danny alluded to.

Quote:

Keeping the FT water level constant is achieved by having a sump tank in the system. Could you explain the relationship between the two? How is this achieved?!

The SLO maintains a constant water level in the FT.

The ST has the pump in it. You pump from there up to the GB's. If the GB's are running as Flood & Drain, then the water level fluctuation will take place in the ST, not the FT

Mr Damage

Vonapster wrote:

MD you quoted....

Match total wet gravel volume with FT water volume at 1:1 ratio, or close to ideally. This is fairly flexible, can be as high as 2:1, or as low as 0.5:1 (most chop and flip IBC systems) and still work effectively.

So if I calculated that I have 1000 litres Total wet gravel volume and using the 1:1 ratio I would need a 1000 litre Fish tank.

If I used the 2:1 ratio then I could get away with a 500 litre Fish tank and with the 0.5:1 ratio you would have a generous 1500 litre Fish tank......Is that correct?

If you are stocking your system to it's max safe fish stocking capacity according to the Wet Gravel:Fish ratio, then the closer you get towards the 2:1 Gravel:Water ratio, the more nutrient you will have concentrated in the water, but the less water you will have per fish in the FT. In that situation, if the water and/or airflow into the FT stops, then any dissolved oxygen in the FT water will decline more rapidly, and any Ammonia spike will occur more rapidly.

I don't like systems being out towards that 2:1 Gravel:Water ratio. I always suggest my customers aim for somewhere between the 0.5:1 and 1:1. Even when stocked to their maximum safe fish stocking capacity they are much more forgiving and healthier for the fish, but still provide excellent plant growth.

earthbound

I've always advised people to get the largest fish tank they can fit and/or afford, then attach grow beds and stock fish levels to the volume of the growbeds.... One of the favourite systems I built had a crazy ratio so far as water volume to growbed goes... A fish tank of about 4000L litres with a tiny growbed of only around 300L or less. Extremely stable system which grew some HUGE silver perch and loads of veg.. This is a pretty crap old video, but you can get a bit of an idea about how huge the fish tank is compared with the GB... And a good idea about plant growth in the system.

Vonapster

Thanks MD on your explanations and diagram.
I’m a visual person when it comes to learning and grasping concepts like this so as soon as I looked at the diagram a light went on in my mind...quite brightly mind you ha ha!

Great advice also on the ratios, it has helped me a lot and feel much more equipped to build my future system when my wife and I move to a bigger property! :headbang:

Thanks for the video link EB! You could almost chuck a line in and have some fishing fun :lol:

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