Backyard Aquaponics
A place to discuss aquaponics

Fish poo wise - I reckon the worms do most of the solids converting into nutrients. The solids are not actually a useable nutrient until they are converted and broken down.

And FINALLY someone else who realizes

Love your goldfish analogy - why cant I put into words what I think

I had heard of aquaponics being 'organic hydroponics', but I'm not sure this is true. Hydroponics is all about control, whereas aquaponics is creating the conditions for nature to excel, hence it's an art. Maybe this is why aquaponics has outperformed hydroponics in studies.

A final thought on this

People who want to optimise the growth of their fish should think about having

- heaps of filtration and plants...the plants will compete for nutes and keep the ppm very low
- a big tank to smooth out spikes

Trying to run massive stocking densities and tiny growbeds will mean nute levels go up. This will optimise the plant growth to the detriment of the fish...yet people who are more interested in fish than vegies always want to increase their stocking densities and decrease their growbeds

I agree they need to be converted, the worms would play a part as would the bacteria. I think all manures and probably all organic matter needs to go through a conversion process before it can be usable nutrients. This is why manures often need to be aged.

Even worm castings may need to be converted?

I believe that the worm castings are the final product, much like chelated iron etc.

Actually I'm very interested in optimizing plant growth (without killing fish).

Tilipia is $2 a kg here, catfish is cheaper and even Barramundi is affordable. But due to the humidity nobody has any luck getting large tomatoes. We've got cooler weather coming up soon so I'm really keen to grow Roman tomatoes for pasta suaces and even bottling.

Besides getting the fish, there's plenty of advantages of aquaponics over Hydro for me. To get the hydro nutrients I have to travel a long way, whereas I can get Tilipia and Catfish down the road. Two inch Tilipia are less than 5c each.

Even in the countryside ppl travel round selling fingerlings for the locals to stock their ponds.

AAAAH! Light bulb moment...... that is why OBO said it doesn't matter cos is a closed system! And hydro isn't!!!

But I still have a question.... I beg your patience OBO!

What is the optimal ratio of fish pond to GB size? I understand that the nutrients will cycle and be absorbed no matter what the sizes but there must be a range where it all happens at optimal levels MORE EASILY.... for both fish and plants. How can this be established if increasing pumping rates can upset the equalibrium? I don't want to use timers to increase or decrease the number of cycles in a day. Does this mean that a system finds its own equalibrium and then you just leave well alone?

I have read somewhere that whatever a GB size it only carries about 40% water cos the rest is GB media.

SO.... would a 7000 litre pond and 3200 litres of water going through GBs be within the optimal range? A good ratio that will help a system find equalibrium easily?

Chelle.. the "equilibrium" is ultimately determined by the amount of filtration capacity in a system....

ie... your filtration capacity can only handle xxx amount of bio-mass (fish) ...

... your filtration capacity (in AP terms - growbeds) will determine the amount of plants...

Both by physical surface area available, and by the filtration capacitys ability to convert nitrogen wastes...

Increasing the volume of the fish tank.... will buy you time.... i.e it will take longer for water quality parameters to exceed limits..

But if you increase your tank size and/or also increase your stocking density... without increasing your filtration capacity ...

Then ultimately you will exceed the capability of the system to process nitrogen wastes...

Resulting in water parameters of pH and ammonia exceeding limits... fish deaths and/or sick/dead plants...

The rule of thumb (not set in stone) is to have twice the growbed volume to tank size... ie a ratio of 2:1 .... to acheive a stocking level approaching 6kg/100ltr...

At 3kg/100ltr... many people successfully run systems with a ratio of closer to 1:1...

There's not an optimal size of tank as such... although the larger the tank volume the greater the thermal stability... and the longer the time to react to water quality issues...

For those reasons... tanks around 2000ltr plus might be preferable... with those around 10000ltr (like many aquaculture recirc systems) probably the optimum...

The temptation with a larger tank volume... is to stock more fish.... even if stocked at the suggested densities....

Then the sheer bio-mass and amount of waste produced means that you need to match the filtration capacity accordingly....

With growbeds as the filtration methology... then physical space may become the limiting factor...

In many ways you need to work backward from your available space (and budget).... determine the amount of fitration capacity you can fit within the area....

Decide whether you want to play it safe and stock at 3kg/100ltr.... and run a 1:1 ratio...

ie 2000ltr of filtration capacity:2000ltr of tank capacity

Or push the stocking density up to 6kg/100ltr and run 4000ltr of growbeds:2000ltr of tank volume.... at a ratio of 2:1 ...

But then at the full stocking rates, and 2:1 GB to Tank size, and 40% of the fishtank water in the growbeds during the flood cycle, you have fish too crowded. So if you are doing the 2:1, you will probably have to flood bed 1, then when it drains, flood bed 2, etc. Otherwise you'll need to teach your fish to walk and breathe air. Alternatively, you can calculate your fish tank volume based on the low-tide amount of water, or make tidal beds (normally flooded, but drained when you pump the water out to the GBs).

A 2:1 ratio system would have a sump... at least 1000ltr for the example above...

But yes you'd probably still be pumping 50% of the fish tank.... probably not a problem if you run Chift Pist....

Thanks Rupe.... Let's see if I understood...


How big GBs are?.... or how much surface area in GBs (ie planting area)?..... or how many litres of water passing through?


yes... got that...


.... so must be surface area that is important and not amount of water carried through the GB .... is that right?


Does this growbed volume you are talking about mean the actual area of the GB? Or the amount of water passing through ?(approximately 40% of the area cos the media takes up about 60%)

I reduced my Fish Pond size right down but it seems like my Fish Pond is STILL even too big cos now 7000litres and my GBs are all 4 x 1 x 0.5.... 4 of them.... adds to 8000 liters.... and take 40% of that as the water passing through....... and I have 3200 litres passing through the filtration system at any one time.... 3200:7000(FT) Wrong way round...

I thought the 2:1 was Fish Pond:GBs! Somehow switched it in my head....

SO I had it backwards.... But this could be OK ... right? Don't really want to go smaller cos of thermal implications for the fish.


Yes.


I will watch my stocking densities.... cos still way too big for the GBs



Rupe, Please tell me if the ratio for the GB is for the amount of water passing through.... or the actual area of the bed...or the surface planting area.

Chelle-
The old adage is 1 gal water, 2 gal growbed, 1 lb fish. - converting to metric - 1 kg of fish -> 9 litres of water, 18 litres of growbed.

This means that 1lb of fish wants at least 1 gal of water, and needs 2 gal of growbed, if you have extra water it just stabilizes your system. The surface area of the growbeds only matter as to the plants that they can support - to a certain extent. (1 ft depth on the growbeds seems to be optimal for bacterial growth for veggies, a Tree might want more depth). There was also a ratio for canopy (I think it was 1 yard of canopy for the same 1 lb of fish - or 2 square meters for the Kilo - but I could be wrong)

Actual amounts vary widely, the biggest things to keep in mind are to not kill your fish by overcrowding for the water, filtration, and Dissolved oxygen. DO is effected by pumping and surface area of the Tank.

It's not the area of the growbed Chelle... it's the volume....

Most people talk of the 2:1 ratio as growbed volume (capacity) : tank volume (capacity)... as a rough rule of thumb... To achieve the necessary bio-filtration capacity

But it's all about the bio-filtration capacity.... so ... given that the actual media occupies about 60% of the actual growbed volume....

Example : 2:1 ratio system...

2000ltr Fish Tank (volume/capacity) and 4000ltr Growbed (volume/capacity)....

So Bio-filtration capacity = 2000ltr Fish Tank (volume/capacity) and 60% x 4000ltr Growbed (volume/capacity) ... => 2400ltr of bio-filtration capacity.....

As the filtration capacity is equal to or greater than the actual tank capacity... you should be able to stock, with a mature system and some management... at around 6kg/100ltr...

The actual volume of water required to fill the growbeds (if they all filled to max at the same time) would be 40% of 4000ltr = 1600ltr....

Add say a 500ltr sump... gives a total volume outside the tank of about 2000ltr.... the capacity of the fish tank....

Using a Chift Pist sump system negates problems with the fish tank fluctuating...

Why do these figures matter.... for oxygenation reasons... both for bio-filtration and for tank oxygenation... is probably (from memory) optimal to turn over the fish tank volume about once/1000ltr/hr....

So for a 2000ltr fish tank, we should turn over the total volume of water about twice per hour...

As we have that volume/capcity moving through the example above... even a timer based system should be able to acheive a turnover of twice/hr.... continuous pumping in a Chift Pist is a no brainer...

The implications are important though in terms of selecting/sizing your pump.... increase your fish tank volume (leaving everything else the same).... means you'd have to increase your pump size/volume to acheive the same turnover....

You can get away with a turnover of once/hr... even turning pumps off at night... as people do....

But not much above 3kg/100ltr IMO...

It's late and I've got my mind scattered in about three different directions... so apologies if I'm not expressing things clearly...

And I'd welcome anyone cross checking the figures....

Thanks greenedo and Rupe...

YES of course the volume.... need some sleep too... meant the volume

So if the volume of my Fish pond is 7000 litres.... then the volume of my GBs should be 14000 litres (what I actually build).... when the growmedia is added it effectively becomes 40% of that volume in water passing through... ie 5600 litres. Is this correct? I want to know what to build as GB size

My GB volume is currently only 8000 litres (the build without anything inside)..... minus 60% for grow media.... so pumps through 40% water - which is 3200 litres - when grow media added. That is 2400 litres too little going through if I want the 2:1 ratio in place.

So my pond is still too large even though I have greatly reduced it from my initial design. I don't want to reduce the size cos of thermal protection for the fish. It is 2m by 2m and at shallow end only 1 m deep and slopes down to deep end of 2 m.... for ease of solids removal up through my venturi... oops! hee! hee!.... up through my overflow..... BTW what was it decided we must call it? SLO? Solids Lifting Overflow?

Cyara,
Don't get too hung up on the 2:1 Growbed to Fish tank ratio. It is definitely an important rule of thumb to keep in mind but if you only stock to the 3 kg per 100 l then the 8000 l grow bed to the 7000 l fish tank should be ok once the system is mature.

Of course since you are planning on the sump, (if you have the space) you could happily double your grow beds and then stock as much as your DO supply can support (probably the 6 kg per 100 l.)

Steem made a comment a while back


I think this is a major factor in why a mature Aquaponics system can out perform Hydroponics. There is likely plenty of mineralization that takes place in this sludge that may never really show up in the samples of fish tank water and could probably explain why AP really does work. Since by a pure hydroponics model, AP could not possibly work.

As to the original questions in the thread. Don't worry so much about dilution since that is more a function of time in a closed system.

What I mean to say. In Hydroponics, you mix up your nutrients and run the system, topping up with plain water for a while and the plants use up nutrients also until you have to dump all the nutrient water with now unknown concentrations of nutrients and mix up a new batch. The TDS meter or whatever you use is only really useful when using a specific mixture since it is only an estimation of strength based on the known conductivity of a particular salt in the mix. My system under normal circumstances reads very low on an EC meter but after salting my system to help with fish health, the EC is off the chart and I can only measure it by diluting a sample with a known amount of distilled water. My plants are still doing fine but if I were to mix up a hydroponics solution to anywhere near a strength that would read that high on the meter, I would kill any plants in a system with it. All that aside since it is really only an illustration of how hydroponics and AP differ. Keep in mind that in a hydroponics system, you will mix the appropriate amount of nutrient for the amount of water your system holds. In Aquaponics, you need to provide enough filtration for the amount of feed (nutrient) you will be putting into your system. In hydro you put it in all at once (unless you have a fancy dosing system) and then dilute over time for evaporation. In AP you slowly build up the nutrients over time by feeding and then hopefully have enough plants to use them up and reach a balance.

You can run a system with only a few fish in an aquarium feeding say 5 buckets of gravel and grow lettuce fine, You could also run a huge tank with the same number of fish and those same 5 buckets of gravel and also grow lettuce. It would just take longer to build up the nutrients in the first place.