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Mechanical filtration of a fish tank with pads

One of the most important aspects of running a successful filtration system is knowing which media to add to your filters. One component that is found in all powered filters is the filter sponge pad.

As any experienced fish keeper can tell you, there are three areas that your filter has to cover. Mechanical filtration is the first step in the process; this is then followed by the biological filtration, and finally chemical filtration.

Mechanical and biological filtration are a must at all times, chemical filtration is often only applied when it is required to do a specific job as in removing medications from the water, or for removing unwanted substances that have been found in the water.

When the water is pulled from the tank into the filter it should be pulled through the sponges that are placed inside. The mechanical filtration will now take place. As the name suggests the sponges will sieve the water, pulling out any solid particles that are present, and them letting the water pass through to the next stage. The solid particles are mostly composed of fish food or fish waste, in a planted tank it could also be leaves that have come away from the mother plant and are decaying.

In many of the larger internal filters and pond filters, the sponges are graded for fine filtration and coarse filtration. The coarser sponges should be placed where the water will hit them first so that they can trap the larger particles that are suspended in the water, then the finer sponges will work in the same way but they will sieve out the finer particles. This is how your mechanical filtration works, with the smaller internal filters, there is probably only one sponge that has to deal with all of the sieving of the water.

After a while the water flow will decrease in your filters, this is because the sponges will start to clog as more and more particles are caught up in them. The only way to clear the sponges is by rinsing them in old tank water to remove any debris. The process of rinsing the sponges should be done on a regular basis; this will increase the efficiency of your filters and will also extend their working life. One of the drawbacks is that the sponges can only be rinsed for so many times before they are worn out, because of this I always replace mine every three months.

The reason that the sponges need to be rinsed in old tank water is that they also provide biological filtration as well. Bacteria will colonize the sponges as the filter matures, the bacteria will then break down any toxins in the water like ammonia into nitrites, and then bacteria will break down the nitrites into nitrates which are less toxic to fish. Sponges are ideal for the colonization as they have a very large surface area for the bacteria to grow on. If the sponges are rinsed in tap water it will kill off your colony, this then means that the filter has to re-populate before it can perform the biological filtration.

If your filter system contains at least 2 sponges, when they need replacing, only change one sponge at a time, this will give your bacterial colony the chance to carry on working until the newly fitted sponge has its own colony of bacteria.

Chemical filtration can also be performed by sponges that are sold specially for this purpose. Carbon sponges will act as a water purifier, removing any medications in the water or discolourants that are in your tank, leaving the water crystal clear. If using carbon sponges, always read the manufacturers instructions. Each sponge can only be used in the filter for a certain length of time, after this they can start leaching toxins back into the water. As soon as the recommended usage time has passed they must be replaced with a new sponge.

Nitrate removing sponges are also available on the market; these are commonly used in the jewel filter systems where the different filter sponges are stacked one sponge on top of another. The nitrate sponge is used for fresh water set ups, it is not recommended to be used in salt water set ups.

A lot of water polishing is also achieved by using a really fine polyester pad at the end of the filter media. The grain of this pad is so fine that it will remove the smallest particles from the water; this will then give your tank water a really clean and bright appearance. As these pads are so fine they will easily clog if not replaced weekly or at the most fortnightly. It is easy to know when they have done their job as a brown coloration will appear on the pad surface. A few years ago the polishing pads were only sold in a disposable format, nowadays they are sold as reusable items, simply rinse them the same as the main filter sponges to de clog them.

The main sponges do not always come cheap, for some of the larger filters, you can pay anything up to 8 pounds (16 dollars) for one sponge, with the smaller filters the price will drop down to 2 pounds (4 dollars) per sponge, but they must be replaced as per the instructions supplied with them.

One way of saving on the costs of the sponges is to buy the large sheets of sponge, and then cut them down to size so that they will fit snugly in your own filter. The sheets of sponge are mainly supplied for the large pond filters, but they are easily adapted and the do the same job in an aquarium filter.

Always remember that when you purchase your filter, read through the instruction manual, this will tell you which order to load the media in your filter. Incorrect loading will lead to inefficiency of the filtration system which will then lead to poor water quality.

Further reading about filters on Aqua-Fish.Net

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