Backyard Aquaponics
A place to discuss aquaponics

Agreed on the Ratio being Grow bed Related to Fish tank, (NOT, grow bed related to complete water volume.)

A 2:1 ratio system That had say 1200 gallons of grow bed, 600 gallons of fish tank and a 600 gallon sump tank (provided that sump tank doesn't house fish) is still a 2:1 system even though the total water volume might equal the total grow bed volume. Such a system is going to be more stable because it has more water.

I also agree that flow rates need to be balanced properly. People with big swimming pools for fish tanks have a real challenge. Just because you might only have 30 fish in that swimming pool doesn't necessarily mean you can get away with only pumping 300 gallons each hour. You actually need to get enough of the swimming pool water filtered and circulated regularly to keep the water quality high. I don't know any exact rules on this one though, I know it has been quite a challenge for a few people trying to run large volumes of water with only limited grow beds and trying to reduce pumping electrical demand.

So perhaps to an extent, the flow rates and volumes need to be related closely with feed rates but only to an extent. Eventually one reaches a point when lowering the amount of flow, where the % of water being filtered/circulated might not be enough to keep the system fresh. Likewise, one can push a system only so far beyond it's normal limits by running more cycles or flow each hour.

I think the indexing valves are a great idea but I must also note that there is a stability benefit to having a sump and extra water capacity.

The only benifit I see with a sump is maintaining fish tank water level, if you want more water volumn simply get a bigger fish tank? I still think water volumn to growbed volume is a better way to compare systems, AP systems revolve around a 3-way ratio of fish volumn to water volumn to growbed volumn. The amount of fish you can keep in a given volumn of water depends upon the amount of filtration capacity, so in theory a true 2:1 system you could have twice the volumn of fish? So if this is true you should have twice the fish and growbed capacity of a 1:1 system?
These are only my conclusions from research I have done and are putting in to practice on my first system which is nearing completion, these may change in the future?

Nope... the 2:1 ratio was suggested in order to provide the necessary filtration... for the suggested stocking density...

People have halved the filtration capacity, and often doubled the stocking density... usually on the false premise,... that the fish are only small when stocked...

IMO... you should always stock to your filtration capacity....

Well, Yes that is what a sump is meant to do, maintain the water level in the fish tank while still being able to flood and drain a larger number of grow beds. Having some extra water volume in the system that is not necessarily counted as fish tank simply adds stability to the system and is kinda a side benefit in a way.

Early on most people tended to ask how many fish can they grow out in a given volume of fish tank. I is a regular challenge to convince people that they should only put as many fish in as their filtration can support. It has often been found that having a huge amount of fish tank and only a small amount of grow bed, even with only a small amount of fish, it can be difficult to get enough water filtered per hour or per day to keep things working well (can be done but it is a balance that I don't know a formula for yet.)

So the 2:1 ratio came about as the amount of grow bed in relation to fish tank that would be needed to stock the max amount of fish possible in a given amount of water without having to resort to pure oxygen injection. Well when you are stocking the max amount of fish in a given amount of fish tank, you can't very well take all that water out of the fish tank to flood your grow beds, thus you need a sump tank with enough volume to take care of flooding those grow beds (well now with indexing valves not as much extra volume is needed.)

I suppose I'm a bit confused. I'm not sure what adding another number to the ratios for figuring things really helps? The most important thing is to have enough filtration for the amount of fish you have and you need enough water in the tank for that amount of fish while still allowing the system to function.

Many people have mentioned that perhaps an even more accurate ratio might be growbed to feed rate and I'll agree that for a commercial operation that is probably a better/more accurate way to measure but for the average backyard operation, I don't think we are weighing fish and weighing out rations by % based on the age of the graded fish and such.

It also seems to me that when people start getting too wrapped up in water volumes, they start getting confused wondering if the grow bed volume is just the amount of water that it takes to flood it or if it's the conversion for the surface area or if it's some other math they don't know about.

Basics
3 kg of fish (total on grow out) can be supported by 100 liters of flood and drain media bed. That 3 kg of fish needs at least 50 liters of water to live in. This is where the 2:1 ratio comes from. Of course you can't have a system with 100 liters of grow bed and only 50 liters of water in the whole system and still flood the grow bed without leaving the fish a bit distressed so any 2:1 system needs additional water somewhere. So the question seems to be, does doubling the water volume with a sump tank cause the system to no longer be a 2:1 system? My answer is no, so long as you are not keeping lots of fish in the sump tank. A sump tank was really meant as a plumbing and water level control device or even just a place for the pump. As soon as you start counting on a particular level of water to stay in a tank to keep the creatures living in it happy, you have to start counting that volume of water as fish tank.

The situations where the total volume of water in a system become important are when you need to figure out dosing of something that gets dissolved in water, like salt. Then you need to know the total water volume of the system.

I'm not thinking of many other equations that require knowing total total water volume. And at the moment I don't know any that require total water volume in relation to grow beds or fish tank volumes or even fish weight or feed rate. One needs to know grow bed volumes to figure out how much a sump tank or fish tank might fluctuate during flood and drain for figuring out needed sump tank volumes or if a sump tank is needed but even that one doesn't really care about total water in a system. What about systems that have some DWC beds or raft beds or settling tanks or swirl filters? Other than for figuring salt dosing, do these water volumes really affect how much grow beds are needed or how much fish one can keep or how much pumping one needs to do per hour? On a backyard scale, I don't really think it does. Not even for figuring pumping does it really change things since it is the water in the fish tank that needs the hourly filtering, since all the other tanks/beds are part of the chain, it should all work out.

To that point directly.

Example a 1:1 system with 1000 liters of grow bed and 1000 liters of fish tank can support up to 30 kg of fish.
30 kg of fish can survive in 500 liters of water through so that system could flood the grow bed directly from the fish tank.

Now say we have 2000 liters of grow bed and still only 1000 liters of fish tank. 2:1 system. That system can support 60 kg of fish but there is not enough water in that fish tank to flood 2000 liters of grow bed and keep 60 kg of fish happy, thus a sump tank or other method of flooding the grow beds is needed.

I suppose in a way, a simple 1:1 system is like a 2:1 system but sump and fish tank built into one and works fine as long as it is only stocked appropriately, problem is that so many people like to stock max for the total fish tank volume (disregarding the grow bed volume) and then run into problems as the fish grow!

The whole question of ratios... and stocking densities... has been vexing me for sometime..

And I really think that people need to step back to the basics... and understand some of the basic inter-relationships...

To put it bluntly... most people just don't understand the inter-relationships... particularly with regard to oxygenation...

And sadly this is often compounded by those that stock low oxygen demand fish such as Tilapia...

The 3kg/100L, with 2:1 growbed:fish tank ratio... was formulated for the flood & drain methodology.... on the basis of passive oxygenation methods.... such as gravity return of water back to the fish tank or sump tank...

To put it simply....

Fish need oxygen... to breathe, to convert feed to protein and energy... this varies with fish species (to some extent)... and with fish life cycle...

Bio-filtration processes... need oxygen for chemical conversion processes... the nitrogen cycle... this varies in relationship to stocking densities... waste production and feed rate...

Suspended matter... solids, algae, micro-organism... need oxygen... Biological Oxygen Demand...(BOD)... this varies in relationship to stocking densities... waste production and feed rate...

The ratios suggested ... were suggested as both safe stocking densities... and optimal oxygenation provision... with minimal supervision or knowledge requirement...

There has been a significant push over the last 12-24 months to either stock higher, decrease the growbed:tank ratio.... or both...

IMO... this has put many systems on the edge of oxygen starvation... and has been the ultimate factor in almost ALL fish kills reported over that period...

And frankly... I've never read of so many fish kills... as I have over the last 12-24 months...

It is that simple...

If your desire is to produce the maximum amount of fish for a given volume of water... then pursuing a RAS aquaculture model, with the pre-requisite knowledge... is the optimal way to go... with massive external bio-filtration, high oxygenation input... and solids removal...

And frankly... I don't think that most people have either the necessary knowledge, capital... or time comitment available... to match their desires... and most will kill copious amounts of fish

To put it simply... and bluntly... if you don't understand the inter-relationships, haven't the time for constant monitoring of your systems, the ability to react within an hour to changes in water parameters or equipment failure, or the knowledge of how to react and rectify the inter-relating factors....

Do yourself a favour... and just stick to the suggested formulas... and you'll have happy, healthy fish and vegetables... and a happy, healthy disposition to aquaponics, and your aquaponic system...

good one rupe
i second.
to be efficient and safe a 2:1:.5 is the safe ratio to get max efficiency...

I give +1 to RUpe but +1 TCLynx particularly.

She has a point for trying to clarify the ratios and what they are for because I too notice that a lot of people don't understand that 2:1. I had to take a little while to figure it out too.

The 2:1 is the method I use and it works very well. [it's the 100L growbed : 50L FT plus 50L ST on my part (the pumping to GB will take 40%, 10% is to cover up for the loss of water in the process)] I prolly would use 1:1 if I was willing to put the pump in the fishtank but I lost a lot of fish last year because the pump nearly drained the FT dry one too many times!! Sump ensures that the Fishtank keeps at Full at all times. i'm sure that if you have like 2:1.5 ratio, like the fishtank ALMOST the same amount as in the growbed but you have a small-ish sump tank for the pump - I think that can work too but I have not trialled it properly yet.

I will give an example with 2 systems (both classed as 2:1 systems) why I believe we should compare water volume to growbed volume for ratio's.

System 1. = 1000L fish tank, 4-500L growbeds filled and drained in sequence.

System 2. = 1000L fish tank, 1000L sump, 4-500L growbeds filled and drained however.

If we use the suggested stocking levels of 3kg of fish to 100L of growbed, system 1 will have 60kg of fish in 1000L of water and system 2 will have 60kg of fish in 2000L of water.

With all other things equal (feed and flow rates etc) system 1 should have twice the nutrient level in the water, and thus plants should grow faster and probably more of them?

Does using the suggested stocking levels in system 1 lead to over stocking? If so the stocking formula should be 3 kg of fish per 100L of growbed and 100L of water, or 1.5kg of fish per 100L of growbed in true 2:1 systems?

In system 1 you can setup filling and draining so the fish tank is only ever drained by 200L and in a contiuous cycle you could just add the extra water to keep the fish tank full.

No, no, no...

The suggested ratios were 3kg/100L... of fish tank.... with a 2:1 ratio of growbed volume to fish tank volume....

ie 30kg of fish in 1000L of fish tank.. with 2000L of growbed...

Doubling your stocking density... doubles your filtration requirement/load...effectively it is equivalent to halving your filtration capacity... sadly many people do both... double their stocking denisty, AND halve their fitration (growbed) capacity...

ie 60kg of fish in 1000L... with 1000L of growbed...

You have to remember that effectively.... the media in a growbed equates to about 50% of the growbed volume... the rest is "flood" water...

So 2000L of growbed volume... actually only represents 1000L of filtration media.... (in essence a 1:1 > water volume:filtration volume)

It's all about filtration... AND oxygenation....

As to nutrient levels... there's always an abundance... throughout the system... and the plants take up all they require... and grow to their max regardless....

Regadless of fish numbers.... if your nitrates are above zero... plant more plants...

If your ammonia and/or nitrites are above zero... stop, or cut back your feed.... or add more growbeds.... or eat more fish (lower density)...

ok wayyy more clearer for me now to

Every where else on the forum(including this thread) relates stocking density to growbed volume!
Anyway I will be relating and comparing growbed volume(filtration capacity), fish stocking density and water volume in my systems and as you say the water parameters will let me know if I get it wrong.

Sorry, but the ratios were always consistantly stated as kg/fish tank volume , with a 2:1 ratio of growbed volume: fish tank volume...

Over the last 12-18 months... people have manipulated those ratios... even going as far as to suggest stocking "numbers" of fish to growbed volume...

Resulting in suggested densities of twice that originally proposed as safe... with half the growbed volume ... i.e 60kg/1000L with a 1:1 ratio....

There have been more fish killed in the last 12-18 months than in total for the previous 2-3 years...

And those that suggest increased densities and decreased filtration ratios... usually can't/don't justify their suggestions... other than perhaps pointing to the fact... that "someone" might have got "away with it".... not with any real understanding of the inter-relationships involved...

If you have the knowledge and understanding of the relationships... and the time for micro-management of your systems.... and lots of supplementary aeration... you might "get away with it"....

So if ammonia, nitrite and nitrates are all zero then this is good? For some reason I thought you wanted high nitrates. My plants are fine but the system is only a week old (previously cycled gravel probably sped things up).