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Fish pond filters types and advantages

Fish pond filters are a very important piece of equipment that are vital for the general upkeep of the water quality in your fish pond. There are a few fish pond keepers that run natural ponds without filters, they rely on a balance of aquatic plants with light stocking levels of fish to keep their fish ponds running but this seems to only work short term, for years of trouble free water, the addition of a fish pond filter is a must. They can be classed as the heart of the fish pond, keeping the water quality as high as possible ensuring that the live stock in the fish pond live long and healthy lives as well as giving the fish pond a nice clean look with clear water at all times.

Many novice fish keepers may not realize just how important that fish pond filters really are, just because the water may be clear and sparkling it does not mean that the quality is guaranteed to be high as there may be dissolved compounds in the water that could be harmful to the fish, fish pond filters are not just designed to remove debris and detritus from the water but they are also designed to remove the harmful compounds and toxins as well.

There are two main functions that the fish pond filter will perform, mechanical filtration and biological filtration. There is a third function that they can perform which is chemical filtration but this is as and when required and not needed all of the time.

Mechanical filtration is performed as the water passes through the fish pond filter, sponges or similar will trap and debris or detritus that is present in the fish pond water, it is very important that this stage of the filtration is performed first, if the debris is allowed to pass further into the fish pond filter it can clog the equipment making it less efficient and eventually stopping altogether. The media used for the mechanical filtration is usually sponges of varying grades, coarser grades of sponge are used to remove the larger particles in the water and these are followed by finer sponges to remove the finer particles, it is also important to place the sponges in the correct order inside the fish pond filter. The coarser sponge needs to be placed in the filter first with the finer sponge after; if these are reversed the finer sponge will clog quickly as it will trap all of the debris without the coarser sponge getting the chance to remove the larger particles.

The sponges will also host beneficial bacteria on their surface area so basically are capable of performing mechanical filtration as well as biological filtration. Periodically, these sponges will need rinsing out to de-clog them as part of routine fish pond filter maintenance. This should never be performed by using mains water but should always involve using water from the fish pond, mains water will kill off most of the beneficial bacteria present on the sponges thus reducing the efficiency of the fish pond filter.

The media inside of the fish pond filter is simple to remove from the casing and replace when cleaned, make this a regular task to keep the filter running efficiently.

Some makes of fish pond filters will also have the capability to pre-filter before the water hits the sponges thus making the sponges less likely to clog so quickly, the pre-filter remove larger particles such as leaves and foliage by straining the water and these are very easy to rinse off and keep clear.

Biological filtration is performed by other media that are designed to have large surface areas to host large colonies of beneficial bacteria. The beneficial bacteria convert the toxins in the water that are created by rotting vegetation, fish waste and fallen leaves and convert them into compounds that are safe to the fish. These toxins are ammonia, nitrites and nitrates which cannot be seen; even if your pond water is crystal clear it does not mean that the water quality is always high. Fish ponds are closed environments with the same water being trapped in the confines of the fish pond, in the wild the water is refreshed and fresh water is passed through the streams, larger lakes contain large volumes of water so the toxins are greatly diluted, in the fish pond the toxins remain until the fish pond filter deals with the problem. The colonies of beneficial bacteria take time to fully colonize the filter media, anything up to 6 weeks so stocking the fish pond before the filters are fully cycled is not a good idea as the fish will suffer from stress or even ammonia burns during the pre-cycle stage. Starter cultures of the bacteria are available to purchase and add these to the fish pond to kick off the cycle.

Typical biological filter media are plastic bio-balls that are designed to have maximum surface area or ceramic rings that are porous and very efficient at housing the beneficial bacteria. These are placed in the next part of the filter chamber after the sponges thus this area should never become clogged with debris so maintenance to the biological media is far less than with the mechanical filtration media. Adding pond plants will aid the filter, the plants consume the nitrates and some of the ammonia thus reducing the bio load on the filter but plants will not reduce all of the toxins.

Basically fish pond filters can be placed into two groups and these are gravity flow fish pond filters (these are sometimes referred to as gravity fed fish pond filters), and pressurized fish pond filters. The size of your fish pond can determine which type of fish pond filter is best for you, knowing the water volume of your fish pond is extremely important as the rate that the filter can handle the water volume pumped through each hour is how fish pond filters are normally rated. Generally speaking the fish pond filter should be capable of filtering the total water volume of the fish pond at least twice every hour. A 250 gallon fish pond should be filtered by a fish pond filter that can deal with 500 gallons of the water every hour. The ratings are based on brand new filters and over time the filters do become less efficient so this should also be taken into account and allowed for when purchasing your filter.

Gravity flow fish pond filters

This type of fish pond filter tends to be in the cheaper price range compared to the pressurized fish pond filters and they are suitable for most sizes of fish ponds, even the smaller ones. They are normally supplied with all of the media required for the filtration. They will require a separate water pump which will be located underneath the water surface, usually situated at the bottom of the fish pond. The water pump sends a flow of water through a pipe up to the filter and when the water leaves the filter box it is allowed to fall back into the pond by gravity alone, this keeps the water flowing constantly.

Bear in mind when pricing up for one of these filters that the water pump will be sold separately in most cases so will increase the costs. If you are using this type of fish pond filter with a larger fish pond you can connect more than one filter in a series by using piping to give you a greater filtration power, two or three of these filters gives you twp or three times the rating of filter overall, this method will increase the running costs as more power is required to run multiple filters so also bear this in mind. It is much cheaper to purchase one larger unit for the task.

Pressurized fish pond filters

Pressurized fish pond filters are a self contained unit and are basically the same as a very large aquarium canister filter. The water is kept under pressure inside the chamber but as everything is in a sealed unit they are very compact and tidy making the task of disguising them in the fish pond parameters much easier. These tend to be more powerful than the gravity flow fish pond filters so do demand a higher price. Most models will come complete with drain valves to remove debris etc. making the filter maintenance much easier plus they are usually sold with a built in UV unit to give that extra sparkle to the fish pond water and keep any pathogens and algae under control. The UV tubes need to be kept clean and the tubes will also need to be replaced as per the instructions supplied with the fish pond filter, usually every 6 months. Once the tubes are past their dates they become ineffective.

Whichever type of fish pond filter that you choose remember that the filter is only as good as the media that it contains, judging a fish pond filter by the size of the chamber does not work, instead check what is inside the chamber, make sure that there is space to add sufficient media and enough chambers to house a variety of media for each specific task.

If you are on a tight budget you also have the alternative of building your own fish pond filter and this has been done by many keepers with great success.

Having read through this article you should have realized that the fish pond filter is basically a chamber that holds media with water pumped into it and allowed to be released at the other end. The chamber can be any container that is large enough to hold your chosen media and water proof, if using plastic containers make sure that they are food grade as some plastics can leach toxins after a period of time. Separate areas can be made in the chamber by using plastic or Perspex sheeting which is held in place by using small blocks and a suitable aquarium sealant, the sheets will need to have holes drilled into them to allow the water to pass through.

Sponges can be purchased in large sheets, these are easy to trim down to fit inside the chamber and all of the different grades are available. The biological media can also be purchased separately so the choice is yours as to whether you wish to use ceramic rings, tubing or plastic bio-balls. Most home made fish pond filters are gravity fed so you will still need to purchase a suitable water pump, the same rating rules apply as with commercial fish pond filters, use a pond pump that can turn over at least twice the water volume per hour and connect the pump to the chamber by suitable piping. This will mean drilling a hole in the side of the chamber but this can easily be done with hole drill bits that are used in woodwork and the piping can then be pushed through. Seal around the hole with aquarium sealant so that it is all water tight and repeat at the other end of the chamber to allow the water to leave the filter and pass back into the fish pond. Test the filter once the sealant has cured overnight to make sure that the water flows through the filter correctly, the outflow must match the inflow or you will have problems, this may mean drilling more holes in the sheeting that separates the media but it is worth doing to get the filter working correctly.

Once you are satisfied that the water flow is correct, the home made filter can be positioned in its final resting place, it is best to place the filter higher than the water surface to allow the gravity feed to work.

Home made filters will still require the same maintenance as commercial fish pond filters so ensure that you can get into the chamber to remove the media for cleaning etc., if the chamber has a removable lid make sure that when it is replaced you can clamp it down to prevent it from flying off once the water starts to flow through.

Hopefully this article has given you some insight int0o which fish pond filter is best for you, shop around and look for the best prices but remember some bargains may not be as good as they seem, don’t skimp on the price if it means you finish up with a fish pond filter that is not efficient at keeping the water quality high enough for your fish to thrive!

Question left on Fri, 4 Apr 2014 09:06:05 by Shawn Tully

I have a pond,dug into clay, @30' X 80' X 4' (avg. water depth), with a trench originally dug (Sept. 2008) another 7' deep X 4' X 15', which I know has partially caved in. I've estimated water volume @62,746 U.S. gallons. I have an aerator which stirs the water very well, which I use a few times a week. The only plants are Cattails. I have had fish (Koi, goldfish) and frogs living in the pond since we built it, but a lot of them died this winter I think from ice covering the pond for 4 months (lack of oxygen) which is not normal (I live in S.W. Ontario, Canada). Before I restock I'd like to install a gravity flow filter. Your article on filters, while informative, raised questions. I am not going to filter pond twice an hour due to volume and cost of electricity. More likely a few times a week, at night when elect.costs are lower. Will this still give me the proper results, or will I be wasting time and money? I have had lots of algae the last couple of springs (2012,2013) which I have raked up from the edge of pond. Any advice will be welcomed

Answer by staff: As you have rightly stated running a filter for that size of pond would involve an enormous set up and huge amounts of power to run it. You would probably be best adding lots of oxygenating plants and continue with the aerator as you already are. To help with the algal problem in the springtime it is possible to add the barley straw bales to combat this problem.