Backyard Aquaponics
A place to discuss aquaponics

A list of the feedback we have recieved thus far with regard to growbed media...


Gravel
Pro
Cheapest of the grow media.
It tends to not affected the PH of the water.
It is free draining (there are very few small bits in it to clog up the works)...
It is heavy enough to keep the plants anchored on breezy days.
wont float away
Readily available.
"Bean river Gravel" is smooth enough to not make any holes in your liner (and that will be with you just dumping the buckets of cleaned gravel in).


Con
It is rough on the hands ('bean' gravel is smoother though, but has a smaller surface area for bacteria and needs a good wash!)
Once a growbed is filled with it , it is as heavy as all hell!
There is a lot of very fine dust which takes a lot of washing to get rid of (the finer sand/grit can lead to blockage problems).


Hydrotron or expanded clay balls
Pro
Very light.
Easy on the hands.
Large surface area for bacterial action.
light and easy to handle
Readily available.

Con
Need to be washed as they run red from the dust.
Tends to float in a flood and drain system
Expensive


Rockwool
Pro

Con
Can get rotten spots and alter pH

shell grit
Pro
Will increse your carbonate hardness and as a result buffer the PH of your system VERY well.
Increases the water hardness.

Con


Scoria
Pro
Huge surface area.
Black scoria will pull pH up slightly

Con
Will break down gradually over time.
Is not readilly available in many states and therefore can be expensive.
Can contain a lot of dust and chips that need to be washed out.
Scoria is hard on the hands.
Red will pull it down slightly.
Scoria is mined only in 1 or 2 states here, so if you are outside those areas it is very expensive due to transport costs.


Water (ie DWC)
Pro
No media to buy, wash etc.
Adds additional constant water volume to system which has many advantages.

Con
Need to ensure a high water turnover rate in beds for oxygenation.
May need to provide seperate solids removal and biofiltration components.

Oasis cubes
Pro
Good alternative to rockwool (no rot or sudden swing in PH).

Con

Perlite
Pro
Cheaper than many of the other options.
Very light.

Con
Can wash away easily
Breaks down into a sand type substance that begins to flow through the system with the water after a while

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Live Beyond also gave us this great bit of information regarding Grow Bed Media:
Why use growbed media?

A. Support for the plant. The plants roots anchor to the media to support in windy and rainy conditions.

B. Allows the plants to take up O2 and exchange CO2.
The main supply of oxygen for the roots comes from the air in the voids between the particles of media. In flood and drain systems, the draining of the growbeds draws air down through the media. Dissolved oxygen is also present in the water. The plants roots give off CO2 which is toxic to the roots so good aeration is important.

C. Helps to maintain even root temperature.

D. Allows the uptake of nutrient and water.
Note: The media may be dried out to stress the plants in order to stimulate flowering and fruiting. (but not to long to stress out bacteria)

E. Allows surface area for bacteria growth.


Particle Size of Media.

The larger the particle size of the media the greater will be the amount of root aeration. However the larger it is the lower the amount of the nutrient rich water held around the particles & between the voids..(hence quicker drying..ie large size gravel.rocks).

If the particle size of the media is small then it will have poor root aeration but much higher water-holding capacity (take longer to dry out..ie perlite/vermiculite).

If you have a mix of coarse & fine media then the fine media will fill the voids between the larger particles resulting in poor root aeration but better water holding capacity..(with a very wet bed there will be an increase chance of fungal diseases).

The most acceptable particle size for media seems to be 8-10mm.

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Great summary!!

It will be handy for newies to also include for each grow media how much of it you need to fill a typical 1000 ltr bed? say 1.8 by .3. For example how many kgs of hydroton do I need to fill in each bed (1.8m by .3m). How many cubic metres of gravel typical 8=10mm.

Then we newies can work out the $$$$. Thanks for your assistance.

Cheers,

Cristina

Chris, 1,000 litres is 1 cubic metre

Not sure on the weight of hydro but normally (sometimes) it will have the volume on the bag (in litres)

EB has done a few systems using trailer loads of hydro so may be able to supply an approx volume figure - what size are the bags???

Chris, typically the bags of hydrton are 50ltr and usually cost $30-$35 per bag...

Can be carried quite easily so I'd estimate they probably weigh about 15kg....

For a 1000ltr you'd need 20 bags.... thus about 300kg of weight in a growbed.... and @ $30 each a total cost of $600 for the twenty bags....

Unless you can get a discount for volume

Water will fill the spaces between the hydroton balls during the flood cycle, about 40% of the beds capacity - roughly).... so that's about 400 lts of water....

All up during a flood cycle that's 700kgs + total weight in your growbed during a flood cycle...

I'm using 20mm gravel and I'm glad I did.
I had to pull down one of my baths the other week - the wooden support was collapsing under the weight. The gravel had a fair amount of solids build up - like a very wet clay. So 20mm is good - less maintenance over time. Also 20mm is cheaper than the smaller stuff.

Are Hydroton and Leca the same thing?

I've found this supply in the UK - http://www.mikewye.co.uk/naturalproducts.htm#leca - which is unbranded LECA, and is only 12p/litre delivered. Is there any reason to go with the posh stuff?

Has anyone looked at both together and seen a difference?

LECA stabnds for light expanded clay aggregate. This is what Hyrdoton is. But not all LECA is Hydroton as there are may different barnd such as Canna- Aquaclay, Hydrogran as well as chinsese brands. All are slightly different. Hydroton is much cleaner than some of the others. Hope this helps.

Disagree with the first summary saying Hydroton floats in a flood drain system - this is only true for the first 24 hours. After that it absorbs enough water to not float anymore so should not be a con, just a note of interest for new users.

We have Hydroton, Pea Gravel and Bluemetal beds at school for comparison. Based on what I have observed so far in setup, planting seedlings and seeds I would go for Hydroton as first choice, gravel as second and gravel as third, don't really like the bluemetal beds at all and have found nothing to make me want to use it over gravel which is the same price. Gravel is definitely the most labour intensive to setup as it needs the most washing but it isn't really that much trouble.

Put a layer of Hydroton(10cm ish) over the top of the gravel. Best of both worlds.

yup

And yup... I had a stright gravel bed... rather than dig it all out... took the top 10cm+ off and layered hydroton...

Benifits of ease of transplanting and seeding... and strong root support...

I've got to say that Maidenwell stuff has my interest ....., buffers at PH 6.4??? Excellent for plants. Being white it would be great for keeping beds coller in the heat and for beds you want to keep warmer do the 10cm hydroton topping,

Hah Chappo... on it's on Maidenwell comes in around pH 5.7... they buffered their system with kilos of shells and have managed to keep it around 6.4....

As a note to newbies reading this thread. When people talk about using gravel with success in AP systems, they are probably talking about using river rock, river pebbles, or some other non limestone pea gravel.

Limestone gravel will buffer a system higher than most people like, in cases where I've tried to help troubleshoot problems limestone gravel or marble chips tend to buffer a system up around 8 or higher which might be just fine for initial cycling of a system but may prove problematic for the plants in the long run.

Another media that I tried and was not liking much for a while but am a bit happier about now is sea shells. My system has river gravel mixed with washed shells, probably about 35% shells give or take 10%. Anyway, In the beginning, my pH stayed between 7.6 and 8. The well water here much of the year has a pH of 8 and for most of the first year the pH never dropped below 7.6. But now my system is getting a bit more mature and I've recorded a system water pH of below 7.6 several times now. Last night, a few hours after adding chleated iron to the system, I measured a pH of 7.2 and I think the system has been hanging around 7.4 lately because of some heavy rain fall negating the need to use well water to top up (part of the system is out where it can catch natural rainfall.)

A note to be ware of with maidenwell, it might have more zinc or copper in it that is healthy for certain types of fish.

I have a few rocks of "Expanded Shale Aggregate" in a fishtank now, doing a canary test before I put it into the growbeds. It's 1/4 the the price of hydroton and supposedly pH neutral. I'll post on my thread here when I have a definite opinion.

FWIW, Worm's way sells it and that is where I got my test sample. A number of concrete aggregate providers sell it in bulk which should be an order of magnitude cheaper than worm's way.

-ellie