In the Beginning:
Once upon a time we only had access to rather primitive forms of filtration for the marine aquarium. Undergravel filters were usually the filter of choice. This required the use of crushed coral or dolomite for the substrate, since sand would be too fine to work with the undergravel filter. These filters were excellent biological filters and did a fairly good job at mechanical filtration. You had to do a good job of gravel vacuuming to prevent any clogging of the substrate, and you were also limited by how much area you could cover with live rock or ornamental corals. Needless to say our success rate with saltwater aquariums was severely limited, and also no one successfully kept corals. The late 70’s saw the advent of the “revolutionary” wet/dry filter. Some of the first models came built into the stand, were made of glass and even had glass panels on the stand. Talk about a nightmare to ship and move around! Early wet/dry filters either used rolls of DLS pad media or a series of trays you filled with dolomite/crushed coral, sort of a drip through undergravel filter. It was the advent of the “dry” portion of the filter that allowed hobbyists to now have massive, highly efficient biological filtration for their saltwater aquarium. The use of the siphon overflow box was a bit of a mystery to most of us until we saw it in action. (It still seems that many hobbyists think it “pulls” the water out of the tank while in truth it is simply an overflow pipe located outside the tank.) One lesson many of us first time users discovered was the mistake of having the return pump’s outlet deep in the aquarium. As soon as the power went off, a back-siphon would start and flood the wet/dry sump and make a mess on the floor. The first couple of times this happened we blamed it on the overflow, we did not realize the need for a check valve or siphon break on the return pump! I also became much more familiar with hole saws and bulkheads to attach the external water pumps of the times. The constant noise of the pump was usually less bothersome than the gurgling sound of the siphon overflow box. Especially to the non-aquaphile in the house!
Dawn of a Revolution:
Not too long after the first wet/dry designs were available, people began to realize that the DLS material was also acting as a mechanical filter and started to look for a better “dry” substrate. Enter the Dupla Ball, now better known as a Bio-Ball. These unique plastic balls offered maximum surface area for the nitrifying bacteria to colonize and also offered good gas exchange. The structure avoided channeling of the water flow and did not trap debris. Soon almost all biotowers were filled with Bio-Balls. Most designs had a floss pad located on a drip tray to trap particulates and to spread out the water flow over the top of the entire biotower. Some designs had an overly complex spinning sprinkler bar in place of the drip tray to disperse the water flow, but most would stop spinning after a few weeks. The wet/dry designs became more elegant and offered room to place protein skimmers and optional submersible pumps to run chillers and/or UV sterilizers. The wet/dry filter spawned the development of the large variety of submersible pumps we have on the market these days. Indirectly I think they also pushed along the use of cabinet stands to hide them. When I started in the hobby we all used metal stands so we could stack two tanks in one place, you couldn’t leave that open space on the bottom empty, you HAD to fill it with another tank. Plus, we mostly kept our tanks in our bedrooms or the basement. With the cabinet stand, the aquarium moved out into the family or living room and had to also be an attractive piece of furniture.
The New Age Arrives:
In today’s market, the wet/dry filter is a victim of its own success. The use of a sump style system became so familiar that other uses were quickly adopted. The first was just a purely open sump with space for an extra capacity protein skimmer. This was called the Berlin Method of filtration after the hobbyist there who first argued to use just the Live Rock as the biofilter and a skimmer to remove excess proteins. The argument was this would decrease the build up of nitrates and the myth of the wet/dry filter as a “nitrate factory” was begun. I would like to point out that this is wrong. The nitrifying bacteria on the bioballs (or Live Rock or Live Sand) are the “nitrate factory” but are only eliminating the highly toxic ammonia wastes from the critters in the tank so they do not all die. Without enough of these bacteria, we could not keep anything alive and wet/dry biotowers offer massive biological filtration capacity with reasonable cost and almost no maintenance. The true nitrate factories are any mechanical filter that traps the excess tropical fish food we place in the aquarium for the live fish. QED: we are the nitrate factory. Obviously having a lot of Live Rock in the aquarium increases the development of the denitrifying bacteria in their anoxic cores, but the Live Rock will produce just as much nitrate as before. My personal rant aside, the wet/dry filters have also been replaced by the development of the refugium style sump filters. These are natural filtration utilizing the sump area to place a deep sand bed for denitrification and an area for the growth of macro algae. This combination will eliminate nitrates and phosphates through natural growth of the macro algae (Cheatomorpha) while also providing an environment for beneficial microplankton to develop for feeding of the saltwater fish and corals. The wet/dry filter or at least a biotower still can offer great function for a Fish Only (FO) aquarium where you would not have enough Live Rock to provide the biofiltration. Just remember to clean the mechanical filter pads frequently and avoid over feeding to keep the aquarium care to a minimum.