Mechanical Filtration

Mechanical filtration is one of the most important aspects of a saltwater tank. It seems simple enough, so it can be easy to overlook and under-appreciate, but your mechanical filtration can have a big impact on how well the tank runs.

Most aspects of saltwater filtration are focused on nutrient control, and it all starts with mechanical filtration. It is the critical first step in nutrient control. The mechanical filtration traps waste, debris, and extra food so that it can be removed from the system BEFORE it breaks down and releases nutrients. By removing that waste before it breaks down, it makes all other aspects of nutrient control much more effective. Because of this, it’s vital that the mechanical filtration is effective and properly maintained. So even if the media isn’t clogged up, it should be replaced every three days.

The main methods of mechanical filtration are:

Filter Sock Holder
Add-on Filter Sock Holder

Filter Socks

Filter socks are a basic but effective method of mechanical filtration. A plastic ring holds the opening open for the water to flow into a fabric tube with a closed end so the water has to pass through the fabric which is what traps everything. The problem with filter socks is that they need to be cleaned constantly which is a bit of a pain over time (it doesn’t sound bad at first). The easiest way is in the washing machine, but that left a lot of fine dust in our dryer which is more than unpleasant. The other common method is to bleach them then give them a dechlorinator bath.

Filter socks come in different pore sizes that will trap different size particles. The smaller the pore size, the smaller particles it will trap, which means it will get clogged up faster. If you have filter socks that are clogging up too quickly, try a larger pore size.

Most manufactured sumps come with filer sock holders. If you build your own sump, there are multiple options for filter sock holders that you can add that just hang on the edge of the tank.

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Filter Cups

Filter cups are an alternative to filter socks designed to fit in filter sock holders. Instead of the sock, they are a plastic cup with drain openings in the bottom. You place filter floss or some other bulk mechanical media into the cup. The effectiveness is a balance between pore size and frequency of maintenance. The more coarse the media is, the longer it lasts between cleanings BECAUSE it is removing less. I would try to avoid using filter cups because they will require more maintenance like filter socks, but they are an option to be aware of, if for no other reason than you can use a cheap bulk media which is cheaper and doesn’t require cleaning the way filter socks do.

DIY Mechanical Filtration Reef Tank
DIY Filter Pad Holder

Filter Pads

Filter pads are a classic and simple method often overlooked since filter socks became the new best thing. The water coming into the sump first flows into a filter pad that traps debris. You don’t usually clean and re-use filter pads, (although you can, to a point), just buy a bulk type and cut it to fit your sump. I would choose this over the filter socks because of the lack of maintenance since you don’t have to clean and re-use them the way you do with filter socks.

Although filter socks come in different pore sizes that allow you to select the best one for your need to balance how often you need to replace them with how small the particles are that they remove, filter pads provide even more options. Not only do filter pads come in different pore sizes as well, they also make it much easier to use multiple pore sizes together so the water goes through a pad that is more coarse before passing through a finer pad. This can provide more effective filtration without the pads clogging up as quickly as a fine pad would when you used alone.

Filter Roller

The newest method of mechanical filtration is a filter roller. This is by far the most expensive and complicated method, but it has some very significant benefits that make it worthwhile. A filter roller is a large assembly that has a very long roll of filter fabric that the water passes through. There are two spools, one holds the new fabric and one holds used fabric. The water passes through the section in the middle and as it gets clogged up, the water level rises which triggers the roller to roll up the used fabric and unroll some new fabric.

The benefits of a filter roller are:
1 – They actually remove the waste from the water column, unlike the other two methods which leave it in the water to rot until you remove it from the water column.
2 – They can last a really long time between you needing to do any maintenance ( a few weeks to a couple of months as opposed to every 3 days with the other two methods).
3 – The costs long term are minimal since it’s just replacing the filter roll which is relatively cheap.

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Below is Bulk Reef Supply’s explanation of filter rollers. Fortunately, more options have been brought to market since this video was made, so the costs and compatibility are even better now.