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For those people setting up new systems, there are just a few things to keep in mind when choosing media.
Primarily, you want media that won't mess with your pH too much. Things like limestone and marble will tend to keep the pH in a system very high due to their calcium carbonate, normally such medias are to be avoided. Shells might not be quite as bad but I still wouldn't recommend them as media, they keep the pH up around 7.6 which is still higher than most plants really like and causes Iron lock out requiring regular additions of Iron to the system.
There are also some medias that have a very low pH tendency, Diotamite or Maidenwell is an example of this. Using such a media will require careful observation and buffering of pH to avoid crashing the bacteria and having terrible ammonia spike.

So before you buy a truck load of the gravel, you might see about getting a small amount to run some pH tests after letting the media soak in water for a while.

FYI pea gravel usually refers to the size of the gravel, not the kind of rock, around here cheap pea gravel is likely to be limestone. Mostly quartz type river pebbles of 1/2" and smaller size are usually a fairly good choice for gravel media. Granite can also be good as can lava rock of appropriate size.
Be sure to wash your gravel before putting it in.

Perlite is generally not recommended as it can be difficult to contain and vermiculite breaks down easily. Of the manufactured hydroponic medias the expanded clay balls of high quality are the only really recommended by many Aquaponics enthusiasts.

Coco Coir, Peat, Sand, wood chips, leaves, and other such medias are generally thought to hold to much water (keep it to wet for the plants) and may also leach undesirable tannins into the water. If trying to use any of these please do it on a small scale in an experimental set up when you can easily take it offline or remove it from the system if something doesn't go right. I once tried wood chips in a small experimental set up and they turned the water so dark that I could not see the fish.

Please add more tips and tricks about media here.

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Ya that happens.  It will clear up.  8.3ph seems a little high for coco coir tho.  did you measure the ph of water before you added it?
is this medium rough for roots during transplanting?  how large are the particles?

AlbertF said:
down here we use black cinder, also known as scoria or lava rock.  its light, porous and cheap.  I can get it by the truckload for $103 or by the 3/4 cubic foot bag for $4.28
No did not pre-measure.  I have another spare water tank -- I will do that experiment.  Before, then after soak.  Good idea.

Daniel E Murphy said:
Ya that happens.  It will clear up.  8.3ph seems a little high for coco coir tho.  did you measure the ph of water before you added it?

Actually, my ph was a bit low in the water, and marble chips helped raise it a bit.  I will keep tabs on the ph and let you know if ph gets too high

Yea, marble or limestone chips will add buffer to your water, I just recommend you add them in a manner that allows you to take them back out if the pH goes up too high.  Mixing marble, limestone or shells into your grow bed media would make it very difficult to remove later if necessary.  I like to hang the buffer material in the fish tank in a mesh bag or something similar.
Yeah.  Probably the marble mixed in the aggregate.  I am giving up on the coco-coir nuggets -- makes the water too brown. Could be because I am running deep beds also.  I run 4" aggregate, 8" coco-coir and 2" vermiculite in my first planter bed.  I will replace the coco-coir with hydroton in remaining 3 planters.  I am prepping the second bed, and think I will run 1" of charcoal between the aggregate and the hydroton. 
One good thing with the coco-coir is that it does get saturated with water and keeps the vermiculite from making its way down to the gravel section and getting drained.  I may consider a thin layer of coco-coir to carry some vermiculite with my hydroton also -- makes it easy to just put seeds in the bed.
I am actually growing some in cut off 2 liter bottels, that is where I added marble.  If I remove 2 liters, marble goes away

coming across some conflict in medium when it come to gravel ... limestone and marble a  no no ... but granite is recommended by most but some say it changes the ph ??

Most aquaponic home gardeners are using media based, flood and drain systems.  A media based grow bed optimally has about 12” of either ½ – ¾” gravel (no limestone or granite!)"

http://theaquaponicsource.com/2010/08/09/aquaponics-how-to-guide-pa...

Some clarification would be appreciated

 

I've been using 1/2" brown river rock successfully for a few years now.  I have also used shells in one system which keeps the pH quite high which I don't really recommend unless your primary goal is going to be to grow watercress along with your fish.  Anyway, I would call 1/2" the small side of acceptable media and there are many who will recommend 3/4" media but it may be harder to find.  3/4" will allow more air space between rocks and will be slower to clog but 1/2" will also work as long as you don't overburden your system and beware of aggressive plants that tend to take over the world and clog growbeds with their roots (banana, mint.)

 

Whatever your media, I recommend getting a sample of it to run some tests on before you go buying a large amount.  Most media also needs washing before you use it or you many experience some temporary (3-6 months or more) pH elevation from the dust on/in the gravel.  Just because a particular media might be inert, it doesn't mean that the dust that might be all over it is safe.  Lava rock sitting next to a crusher machine breaking up concrete and limestone for use in roads is going to pick up a lot of limestone dust which will affect pH if not washed out well.  Also, many of the expanded clay, shale products may need an initial rinse to get rid of oxides that can affect pH initially.

 

Anyway, run some tests, don't just assume that "pea gravel" is going to be fine for you just because someone in another part of the country says they use "pea gravel"  (pea gravel describes the shape, not necessarily the type of stone, here in FL if you call a supplier and just ask for a truck load of pea gravel it's going to be limestone.)  One test you can do is to rinse the media well and then drop a hand full in a cup of vinegar.  If it fizzes, then it will probably keep your pH too high.

 

Media I've heard of people using

River rock (mostly quartz type rocks)

Granite

Lava rock, pumice, scoria

expanded shale

expanded clay

 

The last two choices are manufactured from natural mined materials by heating it.(shale/clay)

I'm interested in what you say about river rock and lava rock. Because Hydroton is small it takes a lot of it to fill the IBCs and, as you say, it becomes expensive. Home Depot carries both lava rock and a decorative river rock. Would both --either? -- work for the grow beds if I fill the top two inches with hydroton? I don't have easy access here in the Keys to large amounts of either but then I'm only filling three IBC beds. 

Hi Michael, Yes, you can top off river rock with hydroton.  Even river rock and lava can be expensive here in FL, especially buying it in little bags at the big box stores....

Michael, if you have a truck, (or a buddy with a truck) you might want to go get your river rock or lava rock from the Conrad Yelvington yard up in Miami.  Filling an IBC with bagged rock is gonna cost a lot!!!

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