I recently decided to try out
the latest rage in nitrate/phosphate
reduction - bio-pellets ( for info
Reef Blog from 7/7/2010). The
vendors of the pellets (I purchased
mine from Warner Marine) all recommend
approx. 1/2 liter of pellets per
100 gallons of water to be filtered.
I usually stick with
recommended amounts - I always
like to err on the side of
caution - so, for my system,
I need around 2-1/2 to 3 liters of pellets.
opinion seems to be that the pellets require
a fluidized media reactor for
maximum effectiveness. That's
a bit of
a problem as there are no (affordable)
fluidized media reactors on the
market that are large enough to
hold four liters.
So what to do? Well, I happened to have a 24"
long piece of 6" cast acrylic tubing
that had originally been
intended as the neck for a DIY
skimmer that never materialized.
It was perfect for a jumbo sized DIY
reactor, instead. Add to that some 3/8" black
and 1/4" clear acrylic
sheet, a few 1/4"-20 nylon
thumb screws, a length of 1/4" silicone
o-ring stock (all of which I had
laying around as extras from previous
projects), and just about all the
material requirements, for the reactor,
were taken care of. The only parts
I had to purchase were a few 3/4"
Sched-40 PVC fittings and two 6" circular
sewing grids from Jo-Ann's
How does a fluidized reactor work?
Before I start on the description
of the build, it might be good to
describe how a fluidized media reactor
functions - skip this paragraph
if this is not new to you. The term
fluidized media comes from the fact
that the media - such as sand, carbon,
GFO, or in this case bio-pellets
- is forced into a fluid like (ergo
fluidized) tumbling motion by the
flow of water through the reactor.
This can only take place if the
water entering the reactor (in
sufficient volume and force) is first
sent to the bottom of the reactor
and then flows up through the media.
The drawing illustrates this principle:
Of course, in addition to the reactor, a pump is required to move the water from the system,
through the reactor, and back to
A little about the design
This reactor would be holding
a relatively large amount of media.
Add that to the fact that bio-pellets
are fairly heavy, and one can assume
that there will have to be a strong
current through the reactor in order
to cause the pellets to enter into
a fluidized motion. Taking this
need for more water flow into consideration, I dimensioned
all the fittings a size larger than
the 1/2" I usually use. I assumed
that 3/4" water lines would suffice
to get the 2-1/2 to 3 liters of pellets moving
I've been building fluidized
reactors for years using the same
basic and very practical design.
It's seen on many commercial
reactors and with good reason.
The design is straight forward,
comparatively simple to build,
and functions very well.
And the component parts
The top consists of a keyhole flange
made of 3/8" cast acrylic sheet.
I like to use black, but any color
will do. I use a template
whenever I need to make a
keyhole flange. Years ago, I
made a set of flange templates
- one for every standard size of
acrylic tubing, from 2" all the
way to 12". The templates are
made from 1/2" MDF and minimize
the effort necessary to complete
a flange. Using a template and
my router table, I can complete
one in less than half an hour. I
have a page on how to make the
check it out.
I used 3/4" female threaded
couplings for both IN and OUT through-leads.
That way, later, I can change out,
the 90deg elbows for straight couplings
if that better suits the installation
Anytime I have a need to glue acrylic
to PVC, I use the two
part epoxy glue Weld-On 40. It
is extremely strong and fairly
easy to work with. I say fairly
easy because you do have to put
a little effort into mixing it
up accurately, as the instructions call for
a 20 to 1 mix - resin to
Viewed from the bottom, you can
see the fittings used below the
top flange. The longer of the two
(water in) is a 3/4" slip coupling.
When the top is placed on the reactor,
it engages (slips over) the central
water feed tubing that leads to
the bottom of the reactor. The "water
out" lead just ends in a short stub
(just a slice of a normal 3/4" coupling
added for strength) beneath the
The bottom grate consists of
a 6" cast acrylic disk mounted on
a short piece of 3/4" PVC tube.
A large number of 1/4" holes were
drilled in the disk to handle the
water flowing up from the bottom
of the reactor. Above the disk,
I added a 3/4" PVC coupling. When
assembled, the open end of the coupling
receives the central tube carrying
the incoming water to the bottom
of the reactor. Below the disk,
I drilled a number of 3/8" holes
in the short piece of tubing to
function as an exit for the incoming
water. I made sure to drill an
equal number of holes all the
way around the tube to alleviate
any chance of dead spots, in the
flow, as the water travels up
through the pellets.
I then placed a flexible plastic
mesh over the top over the bottom
grate. It has very small openings
and keeps the media from falling
through the 1/4" holes in the grate.
You can get the plastic mesh
circles at JoAnn's or Michael's.
The material is called plastic
canvas and is actually available
wherever sewing supplies are
sold. The number 7 mesh seems to
be the only mesh size available.
It seems to be about the optimal
size for bio-pellets, at least
EcoBak pellets I have (from
Warner Marine). The material is very easy to cut to any desired shape.
I got the idea from a thread on
the Reef Chemistry forum on Reef
Central. For those addicted to
shopping on-line, here's a link to a source
on the web:
The upper grate ensures that
media cannot exit the top of the
reactor with the outflowing water.
It is made up of a perforated acrylic
disk, just like the bottom grate,
but the 3/4" PVC coupling is on
the bottom of the disk, not the
top. The couplings - one on the
top of the bottom disk and one on
the bottom of the upper disk - serve
to connect the two disks with the
central tubing and allow the whole
assembly to be taken apart for cleaning,
The short length of tube extending
from the top, fits into the coupling
on the bottom of the top flange.
There is a small o-ring around the
tube which serves as a seal to stop
the incoming water from leaking
into the upper portion of the reactor.
Here is the internal assembly.
It consists of the upper and
lower grates and the connecting
3/4" PVC tube. As described
earlier, the tubing is not glued
in place. It merely slip fits
into the couplings so that the
whole thing can be disassembled
if need be. The plastic canvas
is hanging down on one side
because I hadn't yet fastened it
to the grate. For that I use
very thin nylon fishing line:
The only parts left to show, other than
the main reactor body is the 1/4"
silicone o-ring and the eight 1/4"-20
thumb screws. I used to use 1/8" o-rings but, recently, I experienced
some trouble with leaking reactors.
Since I changed to 1/4" I've had
no further troubles. I make the
o-rings out of stock I get at
McMaster-Carr. I cut it to the
required length and then glue
the ends together with clear
silicone to make the ring.
A 1/4" wide and 1/8" deep
circular groove is routed in the
lower flange for the o-ring to
fit in to. I do this using a
Jasper circle cutting jig. I
describe the jig in the page on
making keyhole flanges.
At this point, I should probably note that
some feel that Sched-80 PVC
fittings should be used on this
type of equipment, instead of
the much cheaper Sched-40
fittings. I can only say that I
have always used the less
expensive material and have
never had a problem of any kind.
And... the completed reactor
When you put it all together
this is what the reactor looks like.
It has a footprint of 8-1/2" and
stands 28-3/4" tall. It
doesn't look especially large in
the pic, but remember that those
hose barbs at the top of the
reactor are 3/4":
In order to keep all the bio-pellets
in this reactor fluidized, I'll
have to utilize a strong pump. I
have an extra Eheim 1262, so I
try that for a while - or, I
just may buy a Mag 9.5 (a 900gph
pump, just like the Eheim). The
are quite reasonably priced and
I'd be able to use the Eheim
somewhere where its extreme
08/09/2010 - Here's a short video showing
the reactor in action. The
reactor contains 2 liters of
Warner Marine EcoBak pellets and
is being run using a Mag 9.5
pump throttled back to approx.
I'll be writing
up a page about my adventure with
bio-pellets - I'll report on
how the pump, reactor and the
pellets themselves, worked out.