The standard method of “purifying” the water for most aquariums has been to use a filter that is separate from the tank. This device, with which I’m sure you are familiar, is a container holding material that (1) traps particles from the water, and (2) has a sufficient surface area for nitrifying bacteria to colonize. This has usually been an enclosed type or “canister” filter.
A more advanced design was the “trickle filter.” This is an open style, relatively large, Plexiglas box containing a drip plate, prefilter, and spherical-type plastic medium. The drip plate would evenly disperse the water onto the prefilter material to trap particles. This in turn would trickle through the plastic medium, where the nitrifying bacteria would colonize and purify by nitrification. With all this “trickling” taking place, oxygen will get pulled into the water, ensuring that the aerobic bacteria remain aerobic.
The trickle filter is an excellent filtering system for fish-only tanks, where you need a large external area for the bacteria to colonize. Also, the open design of the trickle filter allows easy access to the prefilter material. These filters have been used on reef tanks, but most reef hobbyists realize that the bacteria will colonize any porous substrate (the live rock), and that oxygen is provided by protein skimming. The primary concern of reef keepers using trickle filters is that particles and debris get trapped and accumulate in the plastic medium. This accumulated, nutrient-rich debris then provides a food source for micro-algae.
Plastic media can trap waste, causing high nutrient levels—a food source for micro-algae A trickle filter on a reef system would inhibit bacteria from colonizing on the live rock, by maintaining a high flow rate of water through the media and providing oxygen to that immediate area. This would encourage the bacteria to colonize on the plastic media instead of on the rock.
If the plastic media were ever cleaned, the bacteria would die, sending the reef into an ammonia/nitrite cycle. This may cause death of the more fragile species of the reef, and at worst could cause a domino effect that would involve all but the most hardy specimens.
Faced with these two outcomes of employing plastic media, and realizing that live rock is an optimum substrate for aerobic and anaerobic bacteria, many advanced reef hobbyists simply did away with the plastic media. Those who had trickle filters with plastic media in operation would remove small amounts at a time (approximately 10% at every prefilter change once a week), ensuring that an ammonia/nitrite cycle would not occur, and thereby naturally relocating the bacteria to the live rock.
When I started in the hobby, it was recommended to have a trickle filter as described above. As time went on, even though I had live rock and sand and purified tap water, algae eventually became a problem. When I described this phenomenon to a friend, he shared his knowledge of plastic media and recommended the gradual removal of the plastic media. Slowly, the algae problem diminished in my tank. I will admit I was sceptical at first, but he was correct. This has become standard practice with almost all advanced reef keepers.
USING A TRICKLE FILTER AS A SUMP BOX
In perspective, the recommended filtration is still basically a trickle filter, without the media. We can use the box for a sump (to hold and control the water), and the drip plate and prefilter to provide their benefits. The concept is to change the prefilter once a week, to keep it from going “biological” (which could possibly lead to a small cycle), and to confine and remove the nutrient particles.
If you are currently using a trickle filter, you may be able to use it as a sump. It would have to be large enough to accommodate all the water needed for this type of method. Also, plumbing inlets and outlets may have to be added for feeds and drains to and from the protein skimmers, and possibly a main drain for the system.
The following is an overview of the components for a modern reef filter.
Live rock, 1.5 to no more than 1.75 pounds per gallon.
Large protein skimmer capable of turning over water in the tank 6 times per hour.
Easily removable drip plate and prefilter material to clean or change once a week.
Large main pump capable of turning over water in the tank 6 times an hour.
Large sump box providing considerable turbulence, and capable of holding all the overflow of water from the tank, including the “working water.”
De-nitrification areas .
Proper lighting.
Photosynthetic livestock.