Benefits of Wet/Dry Sumps for Planted Tanks

Benefits of Wet/Dry Sumps for Planted Tanks

Wet//dry sumps provide highly effective filtration, and can easily be customized. Sump filtration is more common in marine aquariums, but is a great option for planted tanks as well. Sump filtration may be particularly ideal for high-tech setups, as equipment such as CO2 and sterilizers can easily be incorporated into wet/dry sumps.

​Here we provide a breakdown of what wet/dry sump filtration is, how it works, and what types of freshwater aquariums may be best-suited for this filtration type.

What is a wet/dry sump and how does it work?

A sump is a filtration system that is essentially a separate tank installed under your aquarium. DIY setups are typically made of a smaller aquarium or plastic crate, while commercial setups are sold as a unit.

In a wet/dry sump, water flows down from an overflow box that is plumbed into the main tank and into the sump. Once in the sump, the water trickles into a drip tray, which evenly distributes the water into biological media, usually either BioBalls or ceramic media. This is the “dry” portion of a wet/dry sump.

Subsequently, the water typically collects into a second compartment of biological filtration that is completely submerged – here we enter the “wet” portion. In many setups, the water then flows through a sponge to filter out additional particulates.

The water then collects in a third compartment, where it is pumped back into the tank through outflows. Many freshwater aquarists include a planted refugium into this area, which adds extra biological filtration. The water may also be plumbed to flow through UV or canister sterilizers before being pumped back into the main tank.

For an excellent video illustration of wet/dry sump filtration, check out this video by Solid Gold Aquatics.

What are the benefits of wet/dry sumps for planted tanks?

One of the primary benefits of wet/dry sump filtration is that it adds substantially to the gallonage of the system, meaning that it can handle more bioload. This can be ideal if you’re planning to have a high density of livestock (although overstocking your tank is still not advisable). It may also be well-suited for species such as large cichlids that produce a lot of waste, or for species that are particularly sensitive to ammonia such as discus.

Some aquarists contend that a wet/dry sump allows optimal growth for denitrifying bacteria. These bacteria are aerobic, meaning that they require oxygen to grow. The trickle setup allows for water flowing into the biological filtration to become oxygenated, thus providing more oxygen to bacteria than traditional canister filtration.

Wet/dry sump filtration is also less conspicuous than other filtration methods. Further, other equipment such as heaters, CO2 diffusers, and pH meters can be placed in the sump. This allows a much cleaner look and doesn’t detract as much from the aquascaping as other setups.

A planted refugium can also be added to sump filtration, unlike any other system. This is typically contained in the last stage of the filtration, and provides additional biological filtration. Species such as anacharis and hornwort may work well for a planted refugium as they grow prolifically and don’t need to be rooted. Do keep in mind that a light source is required for a planted refugium.

What are the drawbacks of wet/dry sumps for planted tanks?

One of the primary drawbacks of wet/dry sump filtration is that it is substantially larger than other filtration systems, usually taking up most of the area under the stand. You may also need to customize or remove the doors of your stand such that it’s easier to access your sump for maintenance.

It will also increase CO2 gas-off which means you will need to increase co2 in order to provide your tank with healthy levels. This can also be a benefit, however, as your water will be oxygen rich due to the nature of wet/dry and allow you safely push above the typical 30ppm of co2 to 40-50ppm.

The initial setup of wet/dry sump filtration is much more involved and in most cases more costly than other options. However, for the serious aquarist, this upfront investment is more than worthwhile.

What types of freshwater aquariums are best-suited to wet/dry sump filtration?

Wet/dry sump filtration is about as good as it gets, so is advisable for most planted tanks. However, large aquariums or high-bioload setups may be particularly well-suited. Sump filtration is excellent for high-tech setups with add-ons such as CO2 or sterilization systems, as this equipment can easily be incorporated into the sump.

Tips for wet/dry sump setup

  • Make sure that the flow rate of your outflow isn’t too high. Most freshwater fish species prefer a very gentle current, and aquascaping can be disrupted.
  • Direct outflows downwards for maximum circulation. However, if this is disruptive to aquascaping the outflows can also be directed more towards the surface.
  • A planted refugium in the sump can help to maximize biological filtration.
  • An airstone in the refugium at night can help to maximize oxygenation of the water thus raising ph in preparation for the drop the next day, and keep scum from collecting on the surface.
  • A larger sump is always better, but in general, it should be at least 1/4 the gallonage of the main tank.


Wet/dry sump filtration is the “Cadillac” of filtration systems, and is a great option for planted tanks, particularly high-tech setups. It’s not for the faint of heart, but is often preferred by the serious aquarist.

Have any insights on wet/dry sump filtration? Please leave them in the comments section below!