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DIATOMACEOUS EARTH FILTERS

Diatomaceous earth, the skeletons of diatoms, allows extremely fine filtering, usually down to 1 micron, a level at which many parasites are trapped as well.

This is very efficient filtering, but should, in my opinion, not be used too regularly on a Reef Tank, as it will filter out all of the free floating lifeforms that many filter feeders in your tank require for survival. Tanks always contain filter feeders, and depriving them of the food they require is not a sensible way to run such an aquarium.

If you use a Vortex Diatom, a Marineland, or a System 1 diatom filter, do so infrequently, and not for many many hours in a row. Use them to clean the water after you stir up the bottom, to remove particulate matter that is now floating around, and then clean the filter and put it away for a while. Regular use is, in my opinion not recommended. Of course, in fish-only tanks they can be run continuously.

Suggestions have also been made that the use of diatomaceous earth may add silicates to the water (Thiel 1986, 1988).

That is undesirable insomuch as it may result in the appearance of live diatoms, which will make the tank look really unsightly. To demonstrate this fact, run water through a diatomaceous earth filter for a few hours, and test for silicate both before and after. You will be up for some real surprises.

Some of these filters can be used with powdered activated carbon as well. This is something to consider doing on an infrequent basis : once every 2 weeks, to once a month perhaps, to clean up the water chemically as well. Never use the diatom powder more than once. Clean the filter after each use and throw the powder away. If you let it sit in the filter, it will cake up, and anaerobic bacteria will appear within hours. When you then switch the unit back on, all the noxious compounds in the filter will enter your tank. A most dangerous situation that can lead to many problems, including massive die-offs !

Should you get such a filter for your Small Reef ? My own answer is no. The drawbacks are the filtering out of fine matter that filter filters need, and the possibility that silicates are added to the water and may give rise to live diatoms (for example Navicula, Berkeleya). If you happen to have one, use it very infrequently, and use the types that does not require diatomaceous earth. There are better ways of fine filtering the water that are more efficient.

SAND AND GRAVEL FILTERS

Perhaps the best and certainly the least expensive to set up. A small old aquarium will do (if you don't have one, look in your local bargain newspaper in the pet section, you will find them advertised all the time).

The filter can be set up using a regular canister filter as well, filled with gravel (or sand, although it is probably better to use gravel.

Because sand is finer than gravel, sand filters will filter much finer material out of the water, but not as fine as to remove what your filter feeders need. Gravel is probably good enough and is easier to maintain and clean. Additionally it is unlikely that anaerobics will start in your gravel filter if you clean it regularly, and if water flows through it continuously.

You can use traditional canisters or special canisters, or you can build one yourself, using a acrylic tube that is outfitted with a top and a bottom. Since you will need to be able to access the inside to clean the filter, you must use some device that allows you to do so. A compression nut is usually best. Make sure it is all plastic, or if any metal is in contact with the salt water, it must be 316 SS. If it is not, you should coat it with some plastic liquid paint, or with aquarium silicone.

It is placed in the top or bottom of the cylinder and tightened. When the gravel (or sand) needs changing or cleaning, the cylinder can easily be opened, the filter material taken out, cleaned and placed back in the cylinder.

Although this type of filter may not be in wide use, it is one of the most efficient and also very inexpensive to construct or set-up. Remember to clean it regularly. You must remove the dirt that you have trapped from the system (the total mass of water in the aquarium and what is in the sump of the filter, pipes, hose, etc.).

If you are not handy, or if you do not want to make the cylinder yourself, some can be obtained commercially. Alternatively, use the aquarium with divider method, shown in the diagram.

MICRON AND SUB-MICRON FILTERS

Similar in their effect to the diatomaceous earth filters, micron and sub-micron filters are extremely efficient at cleaning up the water mechanically. They will remove even the smallest matter, especially if one uses the sub-micron (smaller than 1 micron) variety.

They often consist of a canister outfitted with a cartridge, or bag(s), that will not let particles through greater than the size the bag, or cartridge, is rated for, e.g. 5 microns, 1 micron, 0.65 micron etc... (see also diatomaceous earth filters which perform a similar type of filtration but use a different compound, and the reservations about using such filters expressed).

At that level of filtration even parasites are filtered out. Unfortunately so are all organisms and matter that your filter feeders feed on, and need. As already indicated this is not desirable. If you plan to use such a filter, use it only intermittently and not for extended periods of time. It is important to keep in mind also that such filters put a great deal of back pressure on the pump(s) and that you will lose more and more water flow, as the bag or cartridge loads itself with detritus.

Filters of this kind are rated in both nominal and absolute ratings. Nominal simply means that they will effectively remove most of the matter larger than what the filter is rated for, e.g. 90 percent or better. Absolute means that they remove all matter larger than the rating. As you can well imagine the second variety is quite a bit more expensive than the first.

Several standard canister filters can be outfitted with special inserts that act as micron filters. This usually does not make it necessary for most Hobbyists to buy a special unit.

The better ones, however, are filters specifically built for the purpose of micronic filtration. One such example is the Poly-Bio-Marine PSM-1 filter, which can easily be installed in line, and used in conjunction with the PMA-1 filter, the molecular absorption type (see Chemical filtration for more explanations on that type of filtration).

If you install a micron or sub-micron filter in-line, you should pipe it in such a way, that it can be by-passed, by switching valves. This will allow you to run the system without the micron (sub) filters for most of the time, and run the filters only when you want to, for short periods of time.

By leaving the valves that control the in and out to the fine filters slightly open, you will allow some water to go through all the time. This will prevent the formation of anaerobic activity in those canisters. It is even used by some to function as a denitrating filter. When doing so, you must make the water flow through the canister/filter, very slowly.

Since you will also have to be able to clean the filter, you will need a total of three valves to perform this. The illustration clearly shows how to pipe such a system, either with hard pvc pipe, or with acrylic or flexible pvc hose (better).

If you are not sure how to do so, check with someone who does, or call somone in the Hobby you know who can explain to you how to set such a system up.

These filters put a great deal of strain and back pressure on the pump(s) you are using. It is, therefore, a good idea to plan for a pump that can handle that pressure, when setting up the system.

These filters only make sense in a small Reef aquarium if you happen to have one already. I do not recommend it as a integral part of a basic set-up. Save yourself the expense. And if you do decide to buy one, get a good quality unit. The PSM is probably the best you can get and the easiest to service.

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