Media

[TCLynx]

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.

[TCLynx]

I think the 3/4" will be fine for you Rick.  With the 1/2" stuff you have to be careful that you get the stuff that is really 1/2".

I've seen lots of stuff that is really more like 1/2" and smaller which means you have lots and lots of fines to sift out.  The Expanded slate I got they have 1/2" and 3/8" so the 1/2" is at least bigger than 3/8" since that has been sifted out so seems pretty good though I would still get 3/4" if it was available here.

[rick kennerly]

that was kind of thinking in numerical terms.  1 measure of 1/2"  (by weight in lb or area by cu. yard) should have considerably more surface area for bacteria than 3/4 inch.  

However, as TCLynx points out, graded fill products aren't as uniform on the ground as that indicates.  And 3/4 inch will likely have lots of smaller material in it, particularly in a by the truck load situation, as opposed to a sift, grade and bag affair.  

Looking at it another way: it's better to have screened 3/4 and find lots of 1/2 in or smaller in it than to have 1/2 inch and find lots of 3/8 and fine in it.  

George said:

I'm using 1/2 inch expanded slate because 3/4 wasn't readily available.  Why would you prefer 1/2 inch?

rick kennerly said:

Expanded Shale - I'm getting a truck load of expanded shale delivered to my beeyard later in the month, 3/4 inch.  It seems nobody uses 1/2 inch in this area, which is the size I'd prefer.  

[George]

Been there.  You're right.

rick kennerly said:

Looking at it another way: it's better to have screened 3/4 and find lots of 1/2 in or smaller in it than to have 1/2 inch and find lots of 3/8 and fine in it.  

[TCLynx]

Very good way to explain it Rick.