Choosing a Custom Aquarium Filter: Wet/Dry Filters

In our last post, we discussed Canister filters.

As mentioned, three custom aquarium filters to select from when choosing your setup are:

• Hang-on-Back filters (low-end),
• Canister filters (mid-range), and
• Wet/Dry filters (high-end).

When used properly, each one can keep the fish in your aquarium setup healthy, and reduce the work for aquarium maintenance.  

We have one type of filter to review, and that is a Wet/Dry filter.

A wet/dry filter is, by far, the best filter you can put on any aquarium that does not have live plants or coral in it. Wet/Dry filters usually consist of an acrylic box that sits beneath the aquarium. Water is drained from the aquarium and directed to the filter via an overflow box. Overflow boxes can be hung on the back of the aquarium or you can purchase an aquarium with an overflow box built into it already. These are called “reef-ready” aquariums.

The hang-on models are great if you have an existing aquarium that you are adding a wet/dry filter to, but they need to be monitored regularly. A hang-on overflow box works by siphoning water from a box inside the aquarium to another box outside the aquarium and then the water drains down to the filter. If power goes out, the siphon can stop working and will not start itself again once the power is restored. This means that, if/when power is restored, the filter pump will start pumping water from the filter to the aquarium but the drain will not work to drain the water back down to the filter. If this happens, your aquarium will spill over onto the floor until you turn the pump off, restart the siphon, or all of the water is pumped out of the filter.  The built-in overflow boxes are the safest because they will eliminate the possibility of flooding due to power outages but reef-ready aquariums are not available in smaller sizes and are more expensive than their basic counterparts.

Once the water reaches the wet/dry filter it is directed over a “drip-plate”. The drip-plate is a flat plate with many small holes in it designed to change the water flow from one large stream into many smaller streams (like a shower head) and displaces them over a larger area. The drip-plate is usually covered with a mechanical filter pad to trap large particles of waste, keeping them from moving into the rest of the filter. This pad should be changed periodically to ensure proper flow through the filter.

Under the drip-plate is a compartment that holds bio-balls. The drip-plate spreads the flow of water out so that it falls over and through all of the bio-balls evenly. This compartment is where a majority of the filtration occurs. As discussed earlier, the bio-balls are capable of holding a very large amount of beneficial bacteria because of the way each ball is constructed. In a wet/dry filter, the bio-balls are suspended above the water in the filter so they are constantly exposed to air. This means the bacteria will have the maximum amount of oxygen available to them and will allow them to thrive and work more efficiently.

Another benefit of suspending the bio-balls above the water is aeration of the aquarium water. Once the water is broken up by the drip-plate, it passes through the bio-balls as small droplets and hits a network of spikes on the balls as it passes through them. Each time a droplet hits another spike it is broken up and then rejoined with other droplets. This process forces oxygen into the water, which is then collected in a reservoir under the bio-balls and pumped back to the aquarium. It is this capability that makes the wet/dry filter the best choice for your freshwater or marine, fish-only aquarium.

There are, however, a few negatives about wet/dry filters. For starters, they are more expensive than most canister filters. Another issue is size. Most are bulky and only fit in cabinets made for larger aquariums. Wet/Dry filters generally do not have a convenient means of using chemical filter medias either. This problem can usually be overcome with some minor customization by the user or with the addition of a small canister filter.

If you have a freshwater aquarium with live plants, a wet/dry filter will over-produce oxygen and push out the CO2 necessary for your plants to thrive. In a reef aquarium, the bio-balls will over-produce nitrates and can cause harm to your corals and other invertebrate animals. Finally, wet/dry filters do not come with a pump to move the water from the filter to the aquarium. This is because most wet/dry filters can be used on a range of aquarium sizes but a pump is more specific and should be selected based on the aquarium size. When purchasing a wet/dry filter, you must keep in mind that the pump will be an additional cost to your filter purchase.

Once the filter type has been determined, you can turn your attention to other accessories you required types of aquaria you may set up.

Have questions? Contact the aquariums experts at Diamond Aquatics and we will be happy to help.