Cyclic Tasks: Replacing the Filterwool or Automatic Filter Fleece

Table of Contents

This article is part of the “Cyclic tasks” series, intended for beginner aquarists who are looking for the basics of running a saltwater aquarium, or for those who are considering setting up a tank and want to understand the amount of work involved.

In the article What work on the aquarium should be done periodically you’ll find a complete list of tasks, along with links to articles that expand on individual topics.

If you want to learn more about filtration techniques, I recommend going through the articles in the Filtration category on ReefPedia.

Replacing the filter material

Cotton wool is the simplest form of mechanical filtration. It’s placed somewhere on the water inflow in the sump. Cotton wool is usually replaced every day or every other day.

Another solution will be to use a filter sock, which should be cleaned once every few days. 

Currently, the market is dominated by mechanical filtration devices, such as the Smart roller, in which the filter material is on a roll and moves automatically, according to the settings. We change the roll once every few weeks.

Why filter the water?

The idea is to capture mechanical material from the water so that it’s crystal clear.


Replacing cotton wool in a marine aquarium takes only a moment and doesn’t require special skills. If we use a device for mechanical water filtration, replacing the roll will take a bit longer, but we do it every once in a while, even only once per 3 months (depending on the usage of the material).

About the author

Picture of Marek Protasewicz

Marek Protasewicz

Reefkeeping has been my passion for over 10 years now. I love learning. The hobby has taught me many valuable lessons, patience being the best example. Combining work and passion is my path. I run Crazy Coral, a marine aquarium shop, for a number of years. Building this business from the scratch I learnt from my own mistakes at a heavy cost.
Later I managed a project aimed at development of methods for quick growth of Corals in non-natural conditions. The project was carried out by Get Sales, Poland. Presently, I am responsible for distribution strategy at Reef Factory, of which I am a co-founder. The company produces smart devices for marine aquaristics. The last projects I have been involved in are Social Reef and ReefPedia.

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