causes
the


clay


to


expand,

like


popcorn,


and

become

porous.


It

is


light


in


weight,
and
does

not


compact


over


time.


Shape


of


individual


pellet


can

be

irregular


or


uniform


depending

on

brand
and
manufacturing


process.


The


manufacturers


consider


expanded


clay


to


be

an

ecologically

sustainable

and
re
-

usable


growing


medium

because


of


its

ability

to


be

cleaned


and

sterilized,


typically

by

washing

in


solutions
of

white


vinegar,

chlorine


bleach


or


hydrogen

peroxide,


and

rinsing


completely.
A
less


popular


view


is


that


clay


pebbles


are


best


not


re

-

used

even

when


they


are


cleaned,


due

to


root


growth
which
may


enter


the


medium.


Breaking


open


a

clay


pebble


after


a

crop


has

been


grown


will


reveal


this
growth.
Rock

wool
Rock

wool

(mineral


wool)


is


probably


the


most


widely


used

medium

in


Aquaponics.


Rock


Wool


is


an

inert
substrate
for


both


'free

drainage'


and

recirculating


systems.


It

is


made


from

molten


rock


spun

into

cotton
candy-
like


fibers,


resulting


in


a

fibrous


medium

accessible

to


capillary

action

that


is


not


degraded


by
microbiological

activity.


Advantages


are


that


rock


wool

is


light


weight,


free


of


pathogens,


it

has

very


low


CEC
(Cations

exchange


capacity)


making


effluent


water


readily


available,


and

it

comes


in


different


fiber


sizes


and
orientations.

Higher


density

rock


wool

also


improves

the


wicking


and

dispersion

of


moisture


and

effluent
water,

enticing


roots


into

more


areas


of


the


medium,


and

therefore


increasing

effluent


water


fueled


sites

for
premium

plant


production.


After

usage,


rock


wool

can

be

recycled


into

bricks

or


into

new


rock


wool

again,


and
or

incorporated

into

soil


because


it

is


made


of


natural

rocks


and

contains


great


amount


of


fertilizer


left


within

it.
Coir
Coco

Peat,


also


known


as

coir

or


coco,


is


the


leftover


material

after


the


fibers


have

been


removed


from

the
outermost

shell

(bolster)


of


the


coconut.


Coir


is


a

100%

natural

grow

and

flowering


medium.


Coconut


Coir


is
colonized

with


trichoderma


bacteria

which

protects

roots


and

stimulates


root


growth.


It

is


extremely


difficult


to
over

water


coir

due

to


its

perfect

air

to


water


ratio,


plant


roots


thrive


in


this

environment,


coir

has

a

high


cation
exchange,
meaning


it

can

store


unused


minerals


to


be

released


to


the


plant


as

and

when


it

requires

it.


Coir


is
available

in


many


forms,


most


common


is


coco

peat


which

has

the


appearance


and

texture

of


soil


but
contains

no

mineral


content.
Perlite
Perlite

is


a

volcanic

rock


that


has

been


superheated

into

very


lightweight


expanded


glass


pebbles.


It

is


used
loose

or


in


plastic


sleeves


immersed


in


the


water.


It

is


also


used

in


potting


soil


mixes

to


decrease

soil


density.
Perlite

has

similar


properties


and

uses

to


vermiculite


but


generally

holds


more


air

and

less


water.


If

not
contained,
it

can

float


if

flood

and

drain


feeding


is


used.


It

is


a

fusion

of


granite,


obsidian,


pumice


and

basalt.
This

volcanic

rock


is


naturally


fused


at


high


temperatures


undergoing


what


is


called

"Fusionic


Metamorphosis".