Aquaponic Gardening

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Hello there!

Thought I would jump in and talk to all the great Aquapons out there wondering about 

1. safeness of using Growstones super light weight, highly porous recycled glass substrates as a growing medium / biofilter for growing fish and veggies; 

2. preparation time and if the product dissolves in water through time; and/or

3. Growstones R&D efforts towards Aquaponics and/or Aquaculture.

Due to Growstones sand-paper like surface texture, it is understandable that some people may wonder if its surface can damage roots, worms or fish.

Growstones manufacturing process creates round pores inside each aggregate or pebble. This creates a very large surface area, with many smooth-surface pores, ideal for attachment and growth of nitrification bacteria. 

Growstones are pretty much ready to use out of the bag. And no specially long soaking time is necessary. It is a good practice, as in other media to rinse it, and place in the system, let the system run for a while to check pH, water levels, make sure all is well. Slowly adjust for pH as necessary before introducing fish or plants, as would be the case for other growing media. And you should be ready to grow.

But let me talk about how Growstones are actually made from start to finish and the R&D conducted with growing fish with Growstones:

1. Yes. Growstones are made from glass. However, glass pieces/chard or any intact glass is something you will never find inside a Growstone plant. Glass lives in the landfill, where is is crushed by the city. Then it is grind into a super fine powder- like flour. This flour is then mixed with baking soda (natural foaming agent), and a also natural pH buffer, which is calcium phosphate. These are added in very small amounts to the mix, which is 98% powder glass. 

The mix goes into a kiln where all components are melted together. The process is a simple baking process - the glass melts into a viscous mass like honey, while at the same time the CO2 gas gets released from the calcium carbonate and tries to escape bubbling up through the honey-like glass mass. as in bread, the bubbling of the CO2 is what makes the bread-like texture inside and raises the bread. Instead of wheat we use glass flour - no difference.

If any fines are present at the bottom of the growing bed, these would be due to shipping and handling. These fines are nothing but silica grains quite similar or smaller to grains of sand you see in the shallows in the sea where small fish often times can be found going by their own lives. It does not harm the fish in any way.

2. Typically Growstones do not dissolve in water and keep their physical integrity through time. Sharing from my personal experience as a Growstone grower - I grow with Growstones in DWC and Ebb-flow systems and my reservoir tanks are very clean at all times.

3. For the more curious Aquapons looking for alternatives but who really want to know what these alternatives really are (as I would) - I invite you all to check the link below.

The link takes you to a YouTube video showing our fish grown in one of Growstone multiple long term controlled trials at The University of Arizona, in Tucson. We compared the performance of Growstones, bioballs and biobeads, in Aquaculture systems to raise tilapia. It also shows Dr. Fitzsimmons, who was responsible for the trials talking about the fish. 
This link also includes a summary of the results from these trials relative to water quality parameters and fish growth rates. All water quality parameters are good and fish rates in Growstones were slightly superior compared to the other two media tested. 

I encourage anyone to ask me any questions. I welcome the opportunity to answer questions. I would also like to learn more details from growers who have experienced any issues with Growstones. I am here to help. 

Thank you!

Paula Costa 
R&D Director, Growstone

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Hi Paula,

You would need to say what the PH of this product in water will be. Will the carbonates leach into water over time? What is the typical size of this media? Does the media continue to generate this sand over the normal planting and harvesting of plants in Aquaponics?

Hello Harold -

Good points! Thanks for bringing them up. 

pH - When using water with a pH close to neutral, the water pH after Growstones are added will be within the 7.0 - 7.4 range. The value will be closer to one end or the other depending on the volume of water to the volume of Growstones in the system. Higher volume of water -> pH range closer to 7.

Carbonates - carbonates from the calcium carbonate we use as a foaming agent, do leach initially into solution, which is why the pH tends to increase a bit at first. Silica also also leaches out through time into solution.  None of these elements leach out forever from the 'matrix' of Growstones. So the carbonates effect on pH is temporary.
To assure water pH is closer to neutral, regardless of water to Growstones ratios, we have incorporated a pH buffer (less than 1%) that also leaches into solution counteracting the pH raise from the carbonates. 
It is worth mentioning that both calcium carbonate and di-calcium phosphate are OMRI listed 'Allowed'. 

Particle Size - Growstones most commonly used for Aquaponics is the 'Hydroponic Growth Medium' with 1/2" to 1" particle size range.


Sand - if any sand is present it is due to shipping and handling. If you rinse the material before placing it in your grow beds, you should not see any significant increase in sand due to plant handling. These pebbles are not made of steel, but for the range of forces used when growing plants, they do keep intact through time. Unless you use a lot of strength to compress them...

Another thing that might be of interest to know when using Growstones in Aquaponics is the implications of it being so lightweight. This is important because, if the water level on the grow bed is up to the surface of the media, this will displace the Growstones (they tend to float as they are lighter than water). This in turn will displace roots, which is something no grower wants.
However this is easily solved by lowering the water level in the grow bed to about 2 or 3" below the surface of the medium, depending on your plant's root system depth. For shallow roots I would prefer 2". By capillary action, the upper layer above the water level is kept moist (with no risk of drying). This actually induces aerial root growth, which increases the root surface area.

Let me know if you have more questions.

Harold Sukhbir said:

Hi Paula,

You would need to say what the PH of this product in water will be. Will the carbonates leach into water over time? What is the typical size of this media? Does the media continue to generate this sand over the normal planting and harvesting of plants in Aquaponics?

Hello Paula:

I just received my GrowStones and the on reading the “directions” it directs to: “mix one part GS-1 Hydro Stones into 1 to 3 parts of your preferred ‘soil’…” I had not read any comments on mixing GS with soil in all my Internet explorations and would appreciate some additional information on this. I am setting my system in Panamá (where the Canal is, but not in it) and since I am a writer, I decided to write a book on the subject (in Spanish) to help other in our neck of the woods. I am also getting help from some local pros, but with no or just tangent experience in aquaponics… fun, though! John B

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