Undergravel Filters
For many years, undergravel filters have been the top and most efficient filters for saltwater aquariums.
You can’t find any saltwater aquarium that is successful without one.
There are more advanced filtration system nowadays.
You’re right! Filters have evolved! But even if the times have changed, they are still used by many aquarists.
It is still an effective choice for filtration.
But since there are a lot of improvements in the efficiency of filters, less and less aquarist use it because more and more new technology is available.
The Original
The basic ones has a perforated plastic plate that goes on the bottom of the aquarium under the gravel.
Each rear corner of the plate is a lift tube that extends up into the aquarium. Air is pump to the bottom of each lift tube and bubbles that come right back up the tube creating a water vacuum.
The water in your aquarium gets pulled down through the gravel and the filter plate and out the lift tube. Water circulation is then formed from the aquarium down to the gravel.
Your gravel acts as a media when you use this kind of filters. Debris and other particles gets trapped into the gravel and provides mechanical filtration.
When bacteria that breaks down harmful ammonia from in your gravel, it provides an excellent biological filtration. This is why certain kinds of gravel are required for this kind of filter.
The only problem when you use this kind of filters is that it will usually get clogged from the debris that were trapped in the gravel. It needs to be routinely siphoned.
Cleaning will be hard if your aquarium has lots of corals and live rocks sitting on the gravel. This is the reason why this kind of filter is not really suited for a reef aquarium.
Another potential problem is that they tend to be noisy and may not be strong enough to provide enough water circulation in the aquarium. Specially when the gravel clogs.
They also don’t provide chemical filtration. But carbon cartridges are now available that can fit on the lift tubes.
Reverse flow
Reverse flow of water in the gravel in an undergravel filter will prevent clogging. Efficiency of the media will also be maintained.
How do you reverse the flow?
The common way is by adding another filter. Pump the water from the output of a canister filter down the lift tube of the undergravel filter. This can easily reverse the flow of water. Canister filter will also take care of the mechanical filtration for you.
The reverse flow gravel filter provides an excellent biological filtration without the dilemma connected with the original system.
Powerheads
This is one of the major improvements to the undergravel filters. It replaces the less efficient air-driven system.
The powerhead is a small pump that is sitting on top of the lift tube. It pulls the water through the gravel.
It improves filter efficiency and water circulation in your aquarium. What an upgrade huh?
What about aeration? It comes now with a ventura aerator , which introduces air into the outflow.
Reverse flow powerheads are readily available and you can have a reverse flow undergravel filter without adding a canister filter.
The downside - they don’t really provide filtration. They just move the water efficiently.
Fish-only aquariums are the ones that will benefit this type of filter the most. It is not that expensive and provides good biological filtration.
If you are going to use undergravel filters, I would say that the reverse flow is the most efficient. You can use it with powerheads if you’d like or with a canister filter for added filtration.
Return from Undergravel Filters to Common Aquarium Filtration
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