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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 AJ, Expanded clay is still the way to go in my humble opinion. It is a good investment for me so far. I like hydroton...  they are pretty consistently round.  It just so easy to work with too.  I have experimented with adding pea pebbles in with the hydroton but i still prefer it pure.
I think I will slowly replace my coco-coir with hydroton as the coir wears out. Maybe layer with charcoal.  When you use charcoal, what format is it in?
Hi Wolfenhawke:  Charcoal is as yet a less-used medium.  From what I gather Paul makes his own, I just buy hardwood charcoal for BBQ from Lowe's.  Straight up no mixing with anything else so far, smashed so the sizes are smaller than the chunks that come in the bag.  Just got 8 more bags to use with larger planters (my use so far was for an indoor system with 14 small planters).  If you Google "biochar" you can read a lot more about it and how to make some at home.  HTH!  Here's the link to Paul's thread about it: http://aquaponicscommunity.com/forum/topics/charcoal-as-a-media
Thanks Dave.
I had a bag of briquets in an plastic shed for 2 years, and the briquets basically powderized.  I suspect the hardwood would breakdown more slowly in water -- I don't mind taking care of some sludge, but if all my charcoal broke down at once it could be a mess.  I like the hardwood idea.  Noticed a forum subject on charcoal -- will check that too.
The charcoal is not the same as briquets, the source is oak or hickory or other hardwood that is "pyrolized", which means it is heated in absence of oxygen, leaving almost pure carbon.  The regular kingsford or God forbid Match Light (!) is not the right stuff.  
Yea, ya don't want all the nasty stuff that is in the Briquets.  Go for hard wood charcoal.

I found an article about "Biochar as a hydroponic Growing Medium" listed on biochar-media.e7.to but could not access it. I only found the short description which tells about its "superior performance over other types of media"  A friend told me that his tomatoes grew much better with some charcoal on cotton wool. Did anyone test rock wool in combination with charcoal/biochar?

No, but I can tell you that it has been outstanding in the ground here at my home.  My tomatoes in a biochar (10% by weight) bed produced more than double in comparison.  It was convincing enough to me that I stopped doing comparison plantings and now use it in all of my beds and potting mixes.  Everything I plant does very well and I now use no fertilizer whatsoever, only compost and aerated compost tea.  Make some charcoal and give it a try.  Trials with as little as .2 pounds of char per sq ft of surface area have shown significant improvement.  One member here said it spoke to his inner firebug.  It definitely speaks to mine.

Jacob G. said:

 Did anyone test rock wool in combination with charcoal/biochar?

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

Hi George,

Something went wrong with a reply i sent.I was suggesting between you, Dave and Paul a Biochar group or forum topic is a great idea since i can tell this will play a vital role in future AP.

George J. Thurmon said:

No, but I can tell you that it has been outstanding in the ground here at my home.  My tomatoes in a biochar (10% by weight) bed produced more than double in comparison.  It was convincing enough to me that I stopped doing comparison plantings and now use it in all of my beds and potting mixes.  Everything I plant does very well and I now use no fertilizer whatsoever, only compost and aerated compost tea.  Make some charcoal and give it a try.  Trials with as little as .2 pounds of char per sq ft of surface area have shown significant improvement.  One member here said it spoke to his inner firebug.  It definitely speaks to mine.

Jacob G. said:

 Did anyone test rock wool in combination with charcoal/biochar?

Harold, since I'm still systemless, I can't speak to charcoal in aquaponics with any authority but let me tell you buddy, I'm making plans.  I'm stretched for time but it will  come together.  My neighbor built a simple system for making rather large quantities of char so a grow bed full won't be a problem when the time comes - it's just a matter of a storm coming through and blowing down enough urban waste tree wood.  I'm convinced that properly prepared char will harbor many times more bacteria than any gravel can but I suppose that's just a theory of mine at this point.  A friend who has a lot of experience with biological waste water treatment suggested having a charcoal filter plumbed to your system to filter it if necessary in an emergency.  I thought that might be an appealing alternative to water changes for some people.  The charcoal in the filter could then be used to improve a dirt garden since it would be charged with nutrients.   He's quite an idea guy and is sold on char after watching me make it and garden with it for a for a couple of years.  Anyone who is curious about it should give it a try, even if on a very small scale.  The comparisons I did were very interesting and fun.  I'd be happy to participate in any discussion on the subject.  There already is a topic I think.  Cheers.

Harold Sukhbir said:

Hi George,

Something went wrong with a reply i sent.I was suggesting between you, Dave and Paul a Biochar group or forum topic is a great idea since i can tell this will play a vital role in future AP.

George J. Thurmon said:

No, but I can tell you that it has been outstanding in the ground here at my home.  My tomatoes in a biochar (10% by weight) bed produced more than double in comparison.  It was convincing enough to me that I stopped doing comparison plantings and now use it in all of my beds and potting mixes.  Everything I plant does very well and I now use no fertilizer whatsoever, only compost and aerated compost tea.  Make some charcoal and give it a try.  Trials with as little as .2 pounds of char per sq ft of surface area have shown significant improvement.  One member here said it spoke to his inner firebug.  It definitely speaks to mine.

Jacob G. said:

 Did anyone test rock wool in combination with charcoal/biochar?

Update on the coco-coir.  I washed/soaked mine over a period of 10 days or so.  I did a large batch soaking, and further rinsed small batches 5 times.  My tank water is brown colored -- about a "8.0" on the API High Range pH color scale.  The pH is 8.3.  Can't seem to get rid of the color.  They did have a feint smell of coconut (I cook with them, so am familiar) -- nothing else.  Also, passed the taste test for no salt after the rinse :-).
I am using deep grow beds. So, I settled on a layering of 4" gravel, 8" coco-coir, and 2" vermiculite.  Fish are going into the water tanks over the next 2 days.

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