There wasn’t much about the success rate of starting off seedlings in clay pebbles in any of the aquaponics resources I researched, but I thought I would give it a go as transplanting a clay pebble pot straight into an aquaponics grow bed is much less disruptive to the plants than washing soil off the roots and redistributing them in different media.
Whilst I was waiting for my aquaponics system to properly cycle I started off some spinach, pak choi and basil, in the same clay media as my grow bed. I also grew some seeds in soil to monitor the difference. Obviously as the soil has more nutrients after about 10 days the soil plants started to grow much faster, however once in the system the plants in the pebbles were eventually much stronger than the soil plants. I think having all the roots washed and rearranged in pebbles did not leave the plants in a happy mood and in-fact some of the wilted and perished! This did not happen with any of my pebble seedlings.
VERDICT: Start off your seedlings in the same growing media as your system. Plant them in a pot with holes in the bottom so you can pop them straight in your grow bed. Grow them for about two weeks (or until the roots poke out the pot) before putting them in the main bed, and if possible water them with the same water that is in your system BUT only if it is fully cycled.
TIP: A heated seed tray helps development and of course lots of light is beneficial.
Getting started with your aquaponics system is pretty straightforward once you have the know-how. We will be doing a step-by-step guide to setting up a small system soon, but first I thought it would be useful to talk about the science behind getting your system ready for fish and plants.
There are two options for cycling your system, with fish or without. Getting your system ready so that the right bacteria have established to convert the fish waste into plant food is essential before you start any growing, and to make the water safe for the fish. We think fishless cycling is much more straight forward as your are not panicking about levels of ammonia and nitrite shooting up and potentially poisoning the fish in the initial stages. The cycling process usually takes about 3 weeks.
What you are trying to establish is a natural cycle whereby all harmful substances are eradicated:
FISH WASTE (HARMFUL) >>> NITRITE (HARMFUL) >>> NITRATE (PLANT FOOD – NOT HARMFUL TO FISH)
Without fish, you need a way of simulating their waste products in the system. Household ammonia is perfect for this, as fish waste is ammonia-based. You can get it from most hardware stores or cleaning supply places (I got mine from Robert Dyas). Using this method you can control the amount of ammonia in your system precisely, which is also an advantage over cycling with fish. (Some people use their urine but this is more difficult to control and potentially not that pure).
Things you need for cycling:
- Pure household ammonia
- Small pipettes for measuring amount of ammonia you dispense
- Test kit so you can measure levels of ammonia, nitrite and nitrate in the water, plus the PH levels. This API kit has everything you will need.
IMPORTANT: Before you start cycling, test your water. Some tap water already has high levels of Nitrate and is not really suitable for Aquaponic systems (in this case you could collect rain water if you live somewhere with unpolluted rain, or as a last resort you might have to start off with water bought from the supermarket – you can buy 5L canisters for relatively cheap). Always let tap water rest for 24 hours so the chlorine added to UK tap water has evaporated. You can also buy Tap Water Safe products from your local pet shop to make your tap water safe.
Once you have got your ammonia and your test kit just follow these instructions to get going:
- Add ammonia to the tank a few ml at a time until you reach a reading of 3-4 ppm.
- Record the amount of ammonia that this took (probably around 3-6ml depending on your tank size), and then add that amount every other day until the nitrite appears at about 0.5 ppm.
- Once nitrites appear, half the dose of ammonia or just hold off for a while if you are worried about overdosing the tank, the nitrites will probably increase for a while, do not worry about this, it is normal (mine spiked at 4ppm).
- Once nitrates appear at around 10 ppm, and the nitrites have dropped to zero, you can introduce your fish. Mine nitrates went a lot higher than this initally, but up to around 40 ppm is still safe for fish and this number should drop once you plants start to take up nutrients.
WARNING: Be careful with the amount of ammonia you are adding. If you are setting up a small home system DO NOT overdose the system! If this happens you will have to wash everything out and start again which is very frustrating!
This is a graph of what happened in my system, with the PH, Ammonia and Nitrites. As you can see if took a while to settle down and was quite up and down in the beginning:
NOTE: Your PH should stabilise over time, mine was very up and down but eventually stabilised at about 6.8. This is a good level for both fish and plants.
TIP: It is a good idea to start your seedlings off in the media you are planning to use so you can put them straight in the system once the fish are in. So start the seedlings about a week after you start cycling if you can, a heated seed bed and lots of light helps them to stay healthy.
Below is a graph of my system also showing what happened to the Nitrates just for interest. My tap water started with around 40 ppm so this is probably not representative of what would happen in most peoples systems but thought I would include it for interest. As you can see the Nitrate increased, and then the point at which it starts to decrease is after I installed some plants.