Prefilters, the two best and simplest.

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Prefilters, the two best and simplest.

Post  liquidg on 22nd December 2016, 2:13 pm

Over recent years a form of pre filter called the sock has become very popular, mainly due to its simplicity and they seem very functional.
The draw back to the socks is that they have the water smashing into them, this is the problem with them!
All organic material and inorganic material will be pulverised and a small percentage will be pushed through the porous nature of the material they are made of, no mater how good the micron is.
Of the 80 percent you clean from the socks that got caught, potentially 20 percent was forced through.
Now that on the surface seems fine, but if you intend on using bio filtering, you then need to look at what is housing bacteria with your bio media, this equates to mucus!
Much of the material that comes from your refugium, which is not actually a refugium, it's just a term incorrectly used for an area for algae to import/absorb water soluble nutrients, then add on the immense amount of waste from your aquarium that is directed to your socks, all this will add to the potential of blocking the porous nature of purchased products based on ceramic, glass or calcium, all will loose their potential to reduce nitrate in time by using internal socks.
Internal sock means the flow in forced inside the sock, external sock means an area near to the sock has the flow.

These are examples of internal socks. All have varied microns but all will let you down on varied levels.
These pics are from google images

Why internal filter socks let reefers down.
As you can see, anywhere from hundreds to thousands of litres of water are pounding into that sock smashing particles and forcing much through the socks wall, what is caught in that sock, is not all that came to it.
A pic from google images, I haven't used these in many years.

This is roughly the way I make mine.
Choose hole saw size, this is for glass, if using plastic, use metal or timber hole saws.

hole cut

sand holes edges

heat a small section and fit into hole

make flang

cut sections off

both are ready

check to make sure they fit over original pipe

glue on flanges

make sure 90 degree fits

cut length of pipe for settling pre filter/external sock holder

mark ready to cut grooves in pipe

use angel grinder to cut grooves

sand off surface so wadding wil slide on it

ready to use with 90 degree

cut pipe and ninety degree sat in place

The cut in the top of the ninety degree section is for if the wadding is allowed to be completely blocked, to allow for over flow if you are away or what ever,

sock ready to put cut pipe

ready to go


These two can be made in so many varied ways but work the same, the first barrier, the wall of wadding, has a slow flow through it due to such a large area, catching a great deal, the next being the external sock/settling filter, has no direct water directed at it and from this it allows a more softer catching of what the first barrier doesn't catch.
The other reason the external sock works so well, is that once you turn off the water flow to clean the socks, the water level drops below the that exit, stopping anything that may be there from getting past, which is near non existent!

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