First post here, though i would start a discussion on coupled vs de-coupled aquaponics systems. the past 19 years i have seen a lot of system designs and seen the progression of aquaponics systems, this is my breakdown of the two approaches and what i think are the advantages and disadvantages, with some of the more important points expanded on after.
For those not in the know:
Coupled - The plants and the fish share the same water, same pH, same nutrient concentration, same water flow
De-coupled - The Fish culture system and plant culture system are separate, allowing design and control of each system independent of each other.
- Easy to set up
- not as much infrastructure required
- All water is one body, meaning that pH control, water changes etc are done once (easy to maintain)
- Less pumps needed, the flow from the grow beds can be used as the fish tank circulation
- no control over independent pH levels
- limited ability to treat fish in event of disease
- can result in higher levels of suspended solids in grow beds/grow trays due to sharing water
- requires either online remineralisation, which can result in higher nutrient levels in fish tanks, or off line remineralisation which requires extra infrastructure
- Independent control over pH levels, the pH and other water parameters can be optimised for the fish and plants separately
- Fish can be treated in the event of disease without any harm to plants through elevated salinity or other treatments, water can then be exchanged and filtered (through activated carbon for example) before bringing back online to feed nutrient to the plant system
- Plant system can be adjusted for nutrient deficiency, disease issues without harming fish
- Organic or inorganic nutrients can be added to supplement for short falls in nutrient output from the aquaculture system, or in the event that the fish system is being isolated/treated for disease to minimise or eliminate output in plant production
- At start up phase, or after harvesting, if fish are small and feed rates are low, plant system can again be supplemented with nutrient until nutrient output from aquaculture system increases
- remineralisation can be online in the plant growing area for continuous feed of high nutrient water into the plant system (waste can be dumped directly into into remineralisation tank and water overflows to plant system sump)
- finer filtration can be put on plant growing system due to lower levels of produced solids, resulting in higher quality water being sent back to the plants, less blocking of roots, and maintaining cleaner media beds
- You can heat or chill just the aquaculture system instead of the whole system, saving on power due to a smaller volume of water
- Aquaculture system can be put inside and temperature controlled easier, while plants are outside in poly tunnel in cooler climates and not effecting overall water temperature
- potential for much higher output on both sides
- a separate solids/biological filter can be placed on the return to the plants, polishing water and providing more stability biologically to the plants
- higher set up costs
- more infrastructure requirement initially
- potential for slightly higher running costs depending on design and set up
- two bodies of water to test and maintain
- slightly more room required
- higher level of knowledge required to set up and maintain
Independent pH levels -
Fish, generally speaking, like a pH above 7.5, with some exceptions for hardier fish like tilapia that can take it.
a pH above 7.5 maximises growth by matching the pH of the fishes blood closer.
It also provides more alkalinity (recommended levels of 50-70ppm or more) meaning that the pH is not as unstable as it is at lower alkalinity levels, and that bacteria have access to the important carbonates they need for nitrification.
Plants on the other hand, work best a pH levels between 6 and 7 for nutrient availability (generally speaking)
now you can find a happy medium, but you get the best out of both, meaning pH will be less stable, you will have to supplement alkalinity in smaller amounts, so not to push pH too high, but more often, as the alkalinity reserve is depleted quicker and pH become unstable faster.
having the systems decoupled, means you can put both systems at their own pH levels, have them on dosing systems to maintain these pH levels, and not have to worry about fish getting stressed from lower pH or the plants not growing as well from having a high pH water.
On line remineralisation -
In a coupled system this can result in solids getting back to the system and having to be re-filtered out.
As it does in a decoupled system.
And there are solutions for both, but de-coupled systems can handle it better, for a few reasons:
You can have a semi online remineralisation tank that you just top up whenever you drain solids from the aquaculture system, this then overflows into the plant growing/hydroponic system either automatically or manually, and you drain a percentage of the waste at regular intervals (every 15-30 days)
as the solids production is far lower in the plant system, a fines filter, like a sand filter with inert media in it, a static bed filter etc can be placed on the return, which filters water mechanically, resulting in cleaner water going to the plants, but also the biological stability from the filter offers advantages in nutrient breakdown (excess ammonia from incomplete remineralisation for example) this also means media beds stay much cleaner, this is especially important to labour in semi commercial or commercial systems
there are designs for aeration basins that maintain mixing and aerobic breakdown of solids in remineralisation tanks while minimising overflow of said solids to the plants growing system (or back into the coupled aquaponics system) that help here significantly.
Higher output -
we know that remineralisation results in higher output, its been proven, but what isn’t considered is the effect on specific water quality parameters to maximise growth of fish and plants.
You simply cannot optimise growth for both species unless you have a species of fish that like living at the optimal culture ranges for plants, and more importantly, its growth is not affected by those parameters (tilapia would be one of the few)
pH, temperature, conductivity, background nutrient levels, DO and circulation are all factors here.
Disease outbreaks and health issues -
I sincerely hope it doesn’t happen to you, but inevitably it will, mortality and disease are something we have to live with.
firstly, its much less likely to happen with better control over water parameters and biosecurity in both systems, happier fish and plants means better immune resistance and less disease.
This also means you can treat with things that either the fish will tolerate but the plants wont (salt for example) or something the plants will tolerate but the fish wont (chlorine, high levels or ozone, other plant treatments).
Biotech Aquatica advocates for decoupled systems as they allow better control over system parameters as well as higher production overall, but we also help to optimise coupled systems with newer designs, system upgrades and diagnostics of water parameters and operations.
I might have missed some things, but this is more of a conversation starter to see what everyone thinks, and to give you an idea of my design approach and experience.
I hope it can be beneficial to some.