Sponge filters are one of the most under-utilized tools for a new fishkeeper. Most fishkeepers start out with a filter known as a hang on back filter, or a HOB. While they can be suitable for a new fishkeeper, they have a tendency to clog pretty easily and most of the cheap ones break in a few months. Sponge filters don’t have this problem- there is nothing to break, it’s just a sponge on some plastic tubing. Because they are so simple, they are also often much cheaper. For example, I currently have two 55 gallon tanks. One $20 air pump and one $20 set of 4 large sponge filters got me set up for $20 per tank for a good filter, letting me use two in each for extra filtration, or one in each and more for when I need them. The cheapest HOB for a 55 gallon that won’t break in two months for a 55 gallon is around $50.
Before I tell you all about how great sponge filters are, it would help to know what they are. The sponge in sponge filters are not kitchen sponges, and you cannot substitute them. The basic idea of filtration in an aquarium is to give beneficial bacteria a home, to help them out in filtering your tank. A sponge filter gives them a great place to grow, with a lot of surface area because it is so riddled with holes. Chemical filtration is also covered by your bacteria, and the mechanical filtration is covered by the sponge itself- all of the matter floating around the tank gets sucked into the sponge, and gets stuck in it.
Sponge filters aren’t always the best option though. For saltwater tanks, sponge filters aren’t a good option- they just need more filtration than sponges can offer. Some common aquarium fish also don’t do well with sponge filters, such as hillstream loaches, who like high flow that sponges can’t offer, and crayfish, who will rip up your sponge filter or climb up it to escape. That being said, most of the really common fish do great with sponge filters. Bettas love the low flow of sponge filters, as higher flow filters push them around the tank. Axolotls also like sponge filters for the same low flow reason. Sponge filters are also perfect for smaller fish and shrimp- larger filters might suck them up and blow them all around the tank, but sponge filters are safe for even the smallest of baby shrimp and create almost no flow.
So when considering filters, keep sponge filters in mind, as long as:
- Your fish are ok with low flow, and
- They don’t create a lot of waste that sponge filters and water changes can’t take care of
You can also reach out to me through my website if you have any questions.
(image credits: https://marcusfishtanks.com/products/sponge-filter)