Types of UG Filters

There are several Pros and Cons of Undergravel Filters used in freshwater and marine aquariums that you need to know about before you purchase one for your tank.

Undergravel filters are arguably the most frequently sold filters to beginning tropical fish keeping enthusiasts.

They are simply a slotted plastic plate with one or more “lift tubes” that is placed in the bottom of the tank under a sufficient bed of gravel. An air stone or power head is placed in or on the lift tubes to draw water down through the gravel bed where the mechanical and biological filtration actually takes place.

Many DIY aquarists custom make their own undergravel filters from PVC pipe and plastic “egg crate”.

That being said, here are some of the Pros (advantages) and Cons (disadvantages) of Undergravel Filters:

Pros

• Undergravel filters are extremely versitile. They can be used in a goldfish bowl, a 55 gallon tank and even larger.
• Undergravel filters have no moving parts and are easy to install.
• Undergravel filters are very inexpensive compared to other types of filters
• Undergravel filters are reliable
• Undergravel filters are efficient when cleaned on a regular basis
• Undergravel filters provide huge amount of surface area for bacteria colonization
• Undergravel filters are relatively easy to maintain
• Undergravel filters are perfect in tanks used for rearing fish fry.

Cons

• Undergravel filters require regular maintenance to function properly
• Undergravel filters are not recommended for planted aquariums
• Undergravel filters should not be used with fish who dig.
• Export of waste is much more difficult
• Undergravel filters have unavoidavble “dead spots” beneath the filter and in the bed that cause buildups of hydrogen sulfide.
• Undergravel filters usually have higher levels of nitrates and phosphates.
• No separation of mechanical and biological filtration

Some of the cons for undergravel filters have been debated by tropical fish keeping enthusiasts for years; especially the negative recommendation for using them in planted aquariums.
Some fish keepers have no problem raising live plants with undergravel filters, yet others report plants with stunted growth or with plant roots growing underneath the filters causing restricted water flow.

Efficiency does not seem to pose a problem, as long as the filter bed is being maintained on a regular schedule.

The hydrogen sulfide problem can be avoided to some extent by the use of power heads instead of air stones to increase water flow, and by agitating the gravel on a regular basis.

Knowing the pros and cons of undergravel filters before you purchase one for your aquariium can save you a lot of money, or cost you some if you don’t consider all the facts.