Diatoms are basically a single celled organism that feed on silicates in the water which they use to create a protective hydrous silica cell wall. When the diatoms die off they leave behind a shell that is full of minute pores, (some of the pores are as small as 3 microns), but inside the larger pores there are a second, smaller pore (roughly 0.5 microns). This in effect means that the mass of the diatom is mainly formed from empty spaces, ready to trap the smallest of organisms. The empty shells then collect at the bottom, forming a sediment which is known by a couple of names, either Diatomite or Diatomaceous earth.
Because of these minute pores they could be class as microscopic bio balls, hence the great filtration power of them for collecting the minute debris. A word of warning though, if handling the diatomaceous earth, do not inhale it as it can cause lung problems as it will become lodged in the areoles-it is that fine. A dust mask is a must when either replacing or cleaning the earth.
These filters are commonly used in the beer industry and even in some public water purification systems; they are sometimes used in swimming pool filters as well.
Most of the filters on the market work on the vortex system where water is pumped into a chamber that is filled with the earth, keeping it in solution to maximize the surface area of the medium in contact with the water, and a fine carbon is normally run alongside to trap any toxins that are released when the debris etc. is filtered out.
As the diatoms are so fine, I would recommend that a pre-filter is added before the diatom filter to remove the larger debris from the water.
The reason for this is that they can soon become clogged and have to be cleaned out on a regular basis. Continual running of these is not advisable due to the clogging and most aquarists will only run them every now and again to polish the water, probably once a week for each tank.
These filters are so efficient, that not only do they remove suspended algae from the water, thus the superb water clarity, but also they will remove bacteria and are great for removing parasites that are free swimming. Obviously they cannot remove the parasites attached to fish but they can help the fish heal quickly from cuts and abrasions due to the reduced number of bacteria.
White spot is a tremendous problem to many fish keepers, who try to combat it with medication, but this method can have its drawbacks, it could affect other creatures in your tank. Running a diatom filter will dramatically reduce the parasite population, near enough eradicating it, therefore giving the fish more of a fighting chance of a good recovery.
I have used one of these myself in the past and found that running it for three to four hours on one day of the week certainly made a difference to my tank. I made myself get into the habit of rinsing the earth after every use so that it was always there ready to switch on as required.
When these first came out the diatom was a very fine, dry powder that was quite dangerous to use if the proper safety protection wasn’t worn but nowadays the media is dampened down to try to reduce the risk from the dust.
In its raw state diatomaceous earth is a very light and porous rock but when it is powdered down it can have some abrasive qualities so it is even used in toothpaste & some polishing creams, it is even used to make cat litter due to the amount of moisture it can absorb.