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Victories and Defeats Using Grow Lights in Aquaponics

I have been experimenting with grow lights for over 6 months now. I am by no means an expert and have experienced varying degrees of success. We use them for our two aquaponics grow beds, each measuring 60 x 30 x 15 cm. That said when it has worked well we have hugely sped up the growing process and the yield size.

In this blog article I thought I would share why I have been spending so much time experimenting with grow lights, what I have done when it has worked and what I have done when it hasn’t. I have included as many references as I could remember that I have used at the end of the article. This blog is hopefully a good summary of all of them as well as our own wins and losses. Happy reading.

I think like so many other people out there we have been bitten by the self-sufficiently bug. When I first got into aquaponics it was in Malaysia, where everything grows. Quickly. After one month growing in a small outdoor unit I had grown, from seed, 6 good size heads of Pak Choi.

I proudly announced to my wife that I could make us self-sufficient in 6 months when we returned to the UK. Obviously, that didn’t happen. Returning to the UK, in a pandemic, taking on new jobs and raising our 1- and 4-year-old girls kind of took more time than I had appreciated.

Why grow lights can be helpful

It also turns out there is less sun in the UK than Malaysia (especially in October), so I was not going to be producing quite the same yields without some extra help. This was especially the case by October when I had our first prototype up and running. I turned my sights on grow lights. I found plenty of ready-made systems available and a very good guide for how to build your own lighting system from scratch. I opted for something in the middle. Initially I attached the grow lights to a beam which hung over the grow bed. This led to some issues with bolting plants which I will discuss later. With a bit more research I found a number of designs involving suspending the lights from chains. This had the benefit of being able to raise and lower the lights as your plants grow. I knew the range of growth for the plants I was going to grow was not that great, I opted for a design with far less tooling. The grow lighting design has been a lot of fun to play around with- it has been frustrating at times, and as I said I am no expert, but the innovation behind it sits really well with what we out trying to do at The Aquaponics Project.

One of our biggest challenges with using home, glass, aquarium units has been algae growth. The problem is that the light needed by the plants to grow also shines on the tank, and as there are so many nutrients in the system, algae, along with the actual plants we want to eat grow also. Later in the article we will discuss how we have overcome these issues but a central reason for having grow lights is to remove the need for the plants (and often by association the fish tank) to be exposed to natural light.

How our set up works

I think the best advice I have read on using grow lights is to try to replicate the plant’s natural habitat as best you can. Just like plants in the garden need varying amounts of light so will plant under grow lights in your aquaponics system. Remember this and you cannot go too far wrong.

We have found the herbs have grown very well under the grow lights (they need only around 6-10 hours of light a day), our main challenge has been growing our lettuce, rocket and spinach. The rest of this article will be dedicated to these mealtime staples. I still hold onto the promise I made to my wife of never needing to buy bags of salad again!

We start our seedlings in soil and transplant them to the aquaponic grow beds when they are starting to show their true leaves (usually around 2 weeks after first planting them in the greenhouse). We plant 2 or 3 seedlings together, around 10 cm apart from each other.

The types of grow lights you use are important. Normal lights will not work. When selecting our grow lights, as well as the obvious cost factor, there were three other factors we considered while experimenting with different grow lights. Type of light, intensity of light and length of exposure to the light.

Plants require particular colours of light to help them to grow, this is called Photosynthetically Active Radiation (PAR). These colours occur between the wavelengths of 400-700nm. This is a measurement of the quality of light available to the plants. Blue and Red light are the best. Blue light is used more by the plants during their growth stages, while the plants need more red light if they are fruiting.

The current grow lights we are using have 32 red and 16 blue LED bulbs. One future possible change we might make will be to try a system with more blue light, this might be more suitable for our lettuce as we are not seeking for them to go to flower, and see them more as a cut and come-again option.

At different phases of their life plants require different intensity of light. This is called PPF or Photosynthetically photon flux. It is the measurement of the total amount of PAR produced per second. It is measured in micro-moles per second.

We are currently experimenting with the lights on 75% of their potential power. The type of lettuce we have selected grows in more temperate climates, so we did not want to go for full power as in their natural habits they would not be exposed to such intensity of light for 12 hours of the day. This is real guesswork and please do let us know if you have any better ideas!

Finally, when growing a number of plants together we needed to make sure they all received an equal coverage of the light. This is called the PPFD or Photosynthetic Photon Flux Density. This is the amount of photosynthetically Active Photons that land on an area per second. It is a spot check for the amount landing on a given area per second. We also factor in the need to make sure the plants are not too far from the lights. As a rule of thumb keeping the lights no more than 5cm above the topper most plants. This prevents the plants from becoming leggy or malnourished and ensuring the light is evenly distributed.

What we have learnt by failing

The grow lights have certainly been an experiment and as such have brought a number of failures along the way. The first crop was very stringy, the second crop just failed completely. Here are the mistakes we made and how we have adapted.

The first mistake we made regarded the density of light, I began with the grow lights fixed to the ceiling, this was around a metre from the grow bed. I am unsure if the plants gained much from this. They grew long and thin leaves from stringy stalks, they were also quite pale in complexion. They tasted good but there was not much of a crunch and each plant only grew five of six leaves.

For our second attempt we brought the grow lights much closer to the grow beds, around 5 cm from the tallest shoot. There was very rapid growth but after the plants reached 7-8 cm they wilted and died. I think this was caused by over stressing the plants. I came up with a number of possible solutions for this. Firstly, I thought I had failed to take into account the amount of nutrients available for photosynthesis to occur. With more research I discovered that it was not only pH that mattered when making nutrients plant available. The temperature of the water was also important, I think it might have been too low for the enzymes in the plants to take up the nutrients.

The temperature of the tank had been 20⁰C, which I thought was within the 18-26 ⁰C tolerance so in case it was not the low temperature I thought it might have been something to do with the amount of nutrients. I knew from regular water tests that there were more than enough nitrates in the system, but plants also require potassium and phosphates as their other two main nutrients for growth. I had hoped that all of these nutrients would have been supplied by the fish food. However, not wanting to place all of my eggs in one basket, as well as raising the temperature in the system to around 22⁰C I am also adding 10ml of seaweed feed each week which I know to be rich in all the nutrients needed by the plants. I will increase this dosage to 20ml if the plants remain too light in complexion.

The third change I have made is to increase the length of time the plants are exposed to the grow lights. I have increased this to 12 hours a day which seems to fit within the guidelines that most other growers have recommend (anywhere from 10-16 hours it seems). 12 Hours of daylight also seemed to best fit the plants’ natural habitats.

A final issue we have is with the pH of the water in our area. We live on the South Downs which has very hard water. One of the issues we have not yet been able to rectify is reducing the pH to between 6.5-7.0 which would be optimum for our system. We have tried adding organic acids, water changes with Reverse Osmosis Water and adding the Tetraline Hard-Water remover, if you have read this far then thank you and if you could recommend anything you might have tried then please do get in touch.

Our home aquaponics system comes with grow lighting as an optional extra. If you are experimenting yourselves with grow lights, then we hope you have found this article useful.

Good luck with your growing!

In summary, from what we have learnt so far, our takeaway tips would be these:

· Try to match the plant’s natural habitat as best you can.

· Use purpose-sold grow lights with a mixture of red and blue light.

· Keep your lights on for 12 hours a day.

· Have the lights no more than 5 cm above the highest plant.

· Try to keep the temperature of your water from 20-26⁰C.

· Thin your seedlings

· Make sure your system has a good organic feed, regularly added.


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