Building a Pool Aquaponics Filtration System : what worked for us.

Pond filtration setup

Filtering any aquaponics system is challenging because so many variables exist. Almost all systems end up custom designed to a degree.

An aquaponic system will never remain static because the fish grow, and the fish waste rises simultaneously. It takes a measure of knowledge to design a system that allows for the growth of the fish while supplying the necessary nutrients to the plants.

Get it wrong, and one side of the equation suffers. Get it very wrong (fish or plants), and one side collapses, leading to the other’s collapse.

Some systems are more sensitive to change than others, so the reader needs to understand the differences in scale in differing designs. No one method fits all; however, they are all driven by a few absolute constants: waste per kg of biomass per day.

This is diluted in a large body of water like a pool and concentrated in a small IBC system. There are two sides to the water body/ filtration equation, with one side being a problem and the other being an opportunity.

With the mindset of it being a problem, the aquaculturist should look at a less-intensive system with more water per kg of biomass. This will provide a buffer in the water chemistry allowing the fish to enjoy a quality life with less human input.

It is more suited to a hobby setup rather than a fish-farming process.

The opposite side of the equation sees it as an opportunity to harvest the waste from the fish and maximize the return from the plants that can be grown from the waste because it was concentrated enough to use effectively with plants.

The concentrated setup has little leeway for error and is better suited to the experienced person. The more laid-back larger water body process has more latitude for error and is a good beginner setup.

Now that all of that has been said, let’s talk about our setup in the pool; because it started as one type of system…the laid-back version……..and slowly but invisibly converted over to the other more intense version.

The thing to note here is that this was not a simple IBC with a cut-off top growing a few plants.

This was a 50 000 ltr swimming pool that was now a swimming pool aquaponics system with a massive amount of biomass held within it.

Using Pool Filtration for Aquaponics.

This subject needs your attention if you decide to do similar to us. Turning a swimming pool into a fish farm should not be taken lightly because getting things wrong can be expensive, both for the fish and you.

First things first. We decided on NOT USING the existing pool filtration system that was installed.

We never attempted this because we intended for the pool to have some visual appeal, with multiple garden beds sitting on the edge and constant flood-drain systems watering them. We thought the water movement of a swimming pool pump was too aggressive for what we wanted.

As to the efficiency of the process in general, I suppose the pool filter could work…. but I don’t know; I have no experience to share, and I won’t pretend to know.

There are potential opportunities with the backwash plumbing and re-directing it to garden areas. The driving factor would be how heavy the pool is loaded with fish, and how much water is available to replace what was removed.

Seeing the Waste as an Valuable Asset.

We wanted to close the loop within our pool system and capture the nutrients that the fish poo delivered via the edge garden beds and, later, re-direct the nutrients to other areas of the yard as fertilizer.

This secondary redirection only came up as the fish grew to a large enough size to require it, and we had no idea what that looked like in the real world or when to expect it to arrive.

This was a true two-stage process that evolved over time, and an experienced operator would know what to look for at the turning of the stages.

nutrients kept on site through design
Closing the nutrient loop by keeping fish waste for the food garden

Problems Surface When They Need Attention.

It was about year three when the wheels got wobbly on our system. The fish were getting about 750 grams, and the rainbows we had as mozzie control outnumbered the 180ish Jade Perch 100 to 1.

We had a daily feed time late in the afternoon, where we gave them a handful of organic rolled oats and a handful of sweetleaf leaves.

This diet sustained the fish for a good two more years, along with the odd bit of fruit and slice of bread. The water was green, with visibility down about 450mm or 1 1/2 ft or so.

There was no evidence of stress on the fish at all, and all seemed well. We were pushing the limits of the aeration setup but did not know how close to the edge we were.

This can all be seen in hindsight. We were un-trained with a head full of ideas and a pool, and I don’t know if we were pioneers, but there was very little information available on how we were approaching fish growing.

K2 Biofiltration System.

If you have explored methods of treating water through biological means, you most likely have come across using K2 media beds and barrel set-ups.

We researched this extensively and decided that this method was worth installing at some point.

We had a few large poly barrels that had been used for transporting olives, and at 200ltrs or so each in volume, we could construct a decent-sized bio-filtration system reasonably cheaply. We set to work and put the system together.

K2biofiltration barrels
Repurposed olive barrels with K2 media and aeration to treat nutrients in water.

This biofiltration system that we designed and installed was great for taking care of the nitrates and ammonia in the water but was eventually overwhelmed by algae.

This was very experimental, and we would rate it a failure for an aquaponics pool fish growing system. It helped to grow more algae due to the nitrification process.

More plants in the water would help solve this, but cane toads laying eggs and killing fish added to the Jade perch eating all the plants put an end to that idea.

We had to put up with the algae, it seemed.

Rising Algae

If you haven’t figured it out yet, the entire process was never planned out correctly at the start, and we just made adjustments as time passed when a new problem surfaced. Literally.

Algae lives and dies all the time, but where does dead algae go? It sinks. Over time, the pool floor was quite deep with it. Out of sight, out of mind.

The algae settled on the bottom of the pool and mixed with fish poo, and the gasses that were generated within the clumps made them float to the surface.

Once the gasses were released the clump slowly sunk back to the depths.

Some of these clumps were as big as your head, and they stunk. We needed a better system; this is where it got a bit costly.

We were back on the internet researching fish poo and algae to develop some technique to strip out the algae in a way that allowed us to use the stuff on the block. It is another form of fertilizer, so let’s keep it.

This choice forced us towards mechanical extraction methods and eliminated any chemical solution. We arrived at our answer in the form of a drum filtration system.

It was a Draco Solum 16. We solved several problems at once with this unit.

The water supply to the unit was via an air-lift pump that we made with information gleaned from youtube, which operated flawlessly and continuously for several years.

The air supply for the air-lift pump was supplied via a Takatuki Hiblow HP80 low-pressure air pump. This delivered a constant 6PSI to the airlift pump and fed the water to the Draco unit, which then mechanically screened the water and returned the water to the pool.

The 6PSI aerated the water for the fish as it lifted the water high enough to feed the filter and was rated at 75ish watts, so it was acceptably efficient cost-wise.

This all ended up costing quite a bit……but we were so far into this project that there was no turning back.

airlift pump
Feed and return for the Draco drum filter. Image taken at harvest time when nutrient load was greatest.

The drum filter did a great job of pulling out the algae clumps when they drifted across the bottom of the pool towards the pick-up point of the airlift pump.

The waste the drum filter removed made its way along a few lengths of storm-water pipe and spilled into a banana circle.

This worked fantastic for a while. Every solution we had a win with seemed to only be effective “for a while.”

With this dwindling effectiveness, the applied solution would eventually be overwhelmed by biomass waste generation… aka…fish poo.

Every time we thought we had a win, it would only be a few short months until the system would demand another adjustment, and this is precisely what I was trying to say at the very top of this article.

All systems are dynamic, even large ones. It is only the time value that differentiates the two from each other.

banana circles
PVC piping from the drum filter to the bananas

Fish Waste and Worm Farms.

As I mentioned above, the waste from the drum filter made its way to the banana patch via gravity and had a good effect on the plants. The ground was absorbing the moisture as it spilled, and a multitude of earthworms was consuming the waste.

The worm castings became so thick that I was harvesting them weekly, making a brew in a bucket, and spreading it around the yard without worrying about running out. The more I dug it up, the faster the worms created it. It was a great process while I had the time to continually harvest the castings.

Remember….the fish are still growing, and the bigger they get the more they poop.

The more they pooped, the more algae would show up and be removed by the filter, and the more the bananas had to cope.

The result of all of this was that the bananas had trouble fruiting because of nutrient overload, and the fish kept growing—what a mess.

All this trouble came down to the simple fact that the biomass within the system was far too large for the filtration system and the bananas to cope with.

Every system will have a point where the filtration method will become overwhelmed. In this area, I suggest you forward plan with enough capacity to handle double the expected biomass.

We were blindsided by the breeding rate of the smaller fish we introduced into the system for mosquito control, and the drum filter only bought some time.

The Final Wash-up.

If you were to ask if we regret beginning the project, the answer would be a hard NO. The lessons learnt along the way have been wonderful and impossible to find in any class or book.

The gear cost is important to recognize however it was secondary to us because the money, like all other money, was going to get spent on something eventually, and it paid for the education.

The fish have been harvested, and we have many bottles of canned fish on the shelf now. This part of the process was a success.

The pool is being re-configured back to a freshwater swimming pool with a large UV lamp plumbed in to take care of the water, so minimal chemicals will be used.

The drum filter is sitting and waiting for us to decide its fate. It’s an expensive bit of kit, but it does a fantastic job.

In closing, would I recommend this process to anyone? Yes, absolutely but with these notes attached.

  • Limit the fish numbers.
  • Control the smaller fish numbers as they can breed fast.
  • Have the next step up of filtration planned before you are over-run with the current one.
  • Have fun and involve the kids. It’s incredibly educational.
  • Have a plan for the poo. It is great for the garden and worms. Don’t waste it.

That’s it for this post. I hope you get something out of it to help with your system—any questions or comments, fire away. We will get back to you as soon as we can.

Article by Tim Blanch for He is a qualified Permaculture designer.