Aquarium Filtration

Aquarium Filtration

Author: Warren Stilwell
First published in Aquarium World November 2001

There have been many articles written about filtration. Most describe the different types of filtration only. The following information is designed to help you decide which is the best filter for your aquarium. Also covered will be materials and construction methods that work well and cheaply.

There are five main types of filter system commonly used:

Undergravel – A porous plate below the gravel with uplift pipes using air uplift or powerheads to move the water through the gravel.
Box – A plastic or similar container that lives inside the aquarium that circulates water though some type of media using the air uplift method.
External – An external box that sits off the side or back of the aquarium. Usually powered, circulates the water through some type of media and sometimes has a bio-wheel.
Canister – An external container with pump and hoses that sucks water out of the aquarium, passes it through some types of media in the canister, then returns the water back to the aquarium.
Wet/Dry – A canister or box that either lives above the aquarium with a pump that sucks water out of the aquarium into the filter and flows by gravity back to the aquarium, or below the aquarium using gravity and overflow from the aquarium to the filter and a pump to return the water to the aquarium. The water passes through some types of media in the process.

Filtration Types:

There are three main filtration types:

Mechanical – Media that removes large water-born detritus and particulate type matter from the water.
Biological – Bacterial removal / conversion of dissolved toxic waste by-products.
Chemical – Media that removes dissolved chemicals from the water by chemical exchange.

Purpose of a Filter:

Fundamental to the success of a healthy aquarium is the stable aquarium environment made possible by scheduled water changes and filtration. Water changes provide systematic removal of wastes not normally removed by filtration and restoration of a balanced ionic environment. No system exists, despite irresponsible or misinformed claims to the contrary, that can replace water changes.

What a filter will do is keep the aquarium environment stable for longer so that water changes need only be made periodically. The time between water changes and the size of the water change will depend entirely on the size of the aquarium, the quantity and size of the occupants, how densely planted the aquarium is and the quality of the filtration system.

The next section describes more fully how each filter works, its associated costs and advantages and disadvantages.

Improvements:

There is a major improvement to be made to the canister filter and the trickle filter. The other types of filter cannot use the improvement due to their construction and the fact they do not have a powerful enough water pump.

By fitting a prefilter to the canister and trickle filter it is possible to extend the useful life of the biological media. Most advanced biological media manufacturers recommend the media is partially replaced every six to twelve months. If a suitable prefilter is fitted, the particulate matter that clogs the biological media is removed. Therefore the media does not clog and can be used for many years before replacement is required.

An added bonus is the ease of replacing and cleaning the prefilter. There is another major benefit, the organic matter that would normally decompose in the filter for up to a month can easily be removed every few days. The result is less build up of waste products the filter has to process, and the water stays fresher for longer. If water changes are still done regularly the quality of the water will be much higher promoting excellent fish health and happiness. The fish will breed more easily and have healthier fry. Disease risk will be greatly reduced when water quality is high.

The type of filter best suited for a prefilter is the pleated cartridge filter used on swimming pools. The cartridge and housing can be purchased complete and is fitted between the pump and filter, or tank outlet and filter. If used on a canister filter another pump must be fitted prior to the cartridge filter, as the canister filter’s pump will not be strong enough on its own.

These filters are very easy to change and clean. Simply hosing the cartridge every few days will keep it clean enough. Every 2-3 weeks the cartridge can be emersed in a weak solution of bleach to bring it back to new condition. The cartridge is then rinsed thoroughly and left to dry.

The pleated cartridge filter has a typical pore size of 15 microns. This is very small, and will remove all particles that will block biological media. The result is very clean water in the aquarium and much happier fish. Pleated cartridge filters come in many different sizes. A suitable size for cartridge filters is; 1000L/H 12sq feet, 3000L/H 30sq feet, 6000L/H 50sq feet, 12000L/H 75sq feet.

The cartridges have a square feet measure (being a US design) and the above mentioned sizes will ensure that standard aquarium pumps will work. If a smaller cartridge is chosen there will be too much back pressure on the pump resulting in reduced water flow.

Biological Filtration why have it?

In a closed aquarium system, waste products quickly build up to toxic levels. If large daily water changes are performed, or a continuous water change method is used, there is no need for biological filtering as the waste products are always being diluted.

Most aquariums however do not receive water changes often enough to keep toxin levels diluted to where they have no effect. A biological filter is used to convert the toxic substances that build up quickly into less toxic substances which can exist at higher concentrations without being harmful to the fish and plants.

Ammonia, produced by the metabolism of proteins, is the primary waste product from organic sources.

Ammonia and ammonium exist in equilibrium in an aquarium. In aquariums with a PH below 7.0 ammonia is only present in very small quantities, and is mostly ammonium. Ammonium is a relatively non-toxic compound. If the PH is raised above 7.0, ammonium balance will convert to ammonia, becoming toxic. As the PH rises, ammonia becomes more toxic is the pH increases.

Biological conversion of ammonia

Ammonia is converted first to nitrite, and then to nitrate. Both ammonia and nitrite are very toxic at even low levels (0.25-0.5 PPM at PH 7.2-7.4). Nitrate however is much less toxic and can be easily tolerated at levels of 25-30 PPM by nearly all fish and plants. It is important the level of nitrate is controlled by water changes, plants, or denitrifying filter media. At nitrate levels over 50 PPM, fish suffer, and often die for no reason and many plants have their growth stunted. Nitrosomonas convert ammonia to nitrite, and Nitrobacter nitrite to nitrate.

Here is the technical stuff from Seachem’s seagrams.
Nitrosomonas are short gram-negative rod of about 0.8 by 1.5µm. They are obligate chemolithotrophs, strictly aerobic, that convert ammonia (as the ammonium ion) to nitrite. Nitrobacter are also short gram-negative rods, about 0.7 by 1.5µm, strictly aerobic, obligate chemolithotrophs, that convert nitrite to nitrate. Both can function between pH 6.5 to 8.5, although the optimum is about pH 7.5 to 8.0. Thiobacillus are short gram-negative rods, about 0.5 by 2µm, strictly autotrophic and facultatively anaerobic. They require reduced sulfur compounds as an energy source, converting them to sulfate, using nitrate as an electron acceptor to form nitrogen gas. Carbon dioxide is their only source of carbon. In the presence of oxygen, they utilize ammonia. They can function anywhere between pH 2 to 10, but the optimum is between pH 6.6 to 7.2. There are several genera of anaerobic bacteria that utilise organic compounds (methanol, sugar, other non-nitrogenous organics) and nitrate, converting the nitrate to nitrogen. Anaerobic bacteria do not exist in an aquarium as the conditions are not present to contain them. Rather aerobic bacteria perform an anaerobic function if oxygen is deficient by obtaining their oxygen from nitrate.

Ammonia conversion to nitrite:
Acidic conditions:
2NH4 + H2O + 3O2 => 2HNO2 + 2H3O
ammonium water oxygen nitrous acid water

Under Alkaline Conditions
2NH4 + 4OH + 502 => 4HNO2 + 6H2O
ammonia hydroxide oxygen nitrous acid water

Nitrite to Nitrate:
2HNO2 + O2 => 2HNO3
nitrous acid oxygen nitric acid

Nitrate to Nitrogen:
NO3 => NO2 => NO => N2O => N2
nitrate nitrite ammonia ammonia nitrogen
ion ion ion dioxide
Biological Media

Biological media is the substrate that the nitrifying bacteria live on. Technically all parts of an aquarium system can be considered part of the filter, – the glass walls, gravel, pipework, rockwork, plants, and the filter. All these items must be considered as they all have surface area suitable for colonising bacteria.

It may be possible that the aquarium contents may work almost completely as the filter. This is the idea behind the Berlin filter method used on Marine Aquariums. Only living rock is the filter in conjunction with a good protein skimmer.

Media Surface Area

If biological filtration is the only concern, then maximising the surface area of the media is important. Other factors must also be considered however; compacting of the media, channeling of water through it, gas exchange and flow rate.

If the media is too fine, it may block up, and also gas exchange may not occur efficiently. If it is too coarse, there may not be enough surface area.

Sizing the Filter:

When designing a filter, the first thing to consider is how fast the water will travel through the media. For a given cross-section of filter media there is an optimum flow rate.

A good guideline is:
1. For very porous media with a large total surface area:
500L/hour for 100mm x 100mm of media. The depth of the media should not exceed 150mm.
2. For open media like bio-balls:
150L/hour for 100mm x 100mm of media. The depth should not exceed 600mm.

E.g. using porous media for a flow rate of 6000L/hour:
6000 / 500 = 12, so we need 12 x 100mm x100mm of surface area.

If 300mm x 400mm cross-section is used, 150mm deep, it will house 18L of media (300x400x150 / 1000000 = 18L). This is a lot of media, so the depth can be adjusted to reduce the amount of media to suit the size of the aquarium and the biological load. If a relatively efficient media were used, e.g. Siporax, 18L would suit an aquarium up to 3600L going by the manufacturer’s specifications. 6000L/hour suits an aquarium of 1200-1800L, so only 9L of substrate is required, dropping the depth of media to 75mm.

The media chosen often has an optimum number of liters it was designed to filter. Use this information plus experience from your local fish shop or club to help decide if you will need more or less than the manufacturer recommends. From the flow rate required to filter the aquarium (usually between 3-6 times the total tank volume per hour) work out the cross section of filter required.

If you are buying a canister filter, these often come with media. Do not choose a filter too small. If in doubt, go one size up.

Biological Load

The larger the biological load, the more filter media will be required and the more regular and larger the water changes will need to be. More efficient media will reduce the size of the filter for a given biological load. A more efficient filter design will reduce the media requirements also. Trickle filters tend to be amongst the most efficient biological filters. When combined with efficient biological media, a trickle filter can be physically quite small.

Media Types – A Comparison

Bio Balls

Description: There are many types of these. They are all quite similar having an open design with a hard non-porous surface. Usually made from plastic, having lots if spikes or ledges. Usually spherical in shape.
Surface Area: Small surface area.
Advantages: Does not clog. Has massive open air spaces for oxygen when used in trickle filters. Best-used in trickle filters.
Disadvantages: Small surface area requiring a large volume filter. Not good in canister filters.
Cost: Very Cheap to Medium Expensive depending on brand.
Best Use: Large Trickle Filters, In Filter Sumps

Eheim Effisubstrat

Description: A whitish synthetic glass-epoxy chip. Air is injected into the substrate as it is made creating microscopic cavities inside of approx 5-50um. Very suitable for bacterial colonisation on a massive scale.
Surface Area: Large, approx 450m2 per liter of media
Advantages: High Density bacterial colonisation, making the size of the filter small. Very effective in canister filters.
Disadvantages Clogs easily, required a good prefilter. May not allow enough air between each chip for maximum efficiency in trickle filters. Medium / High Cost
Cost: High, but offset by less required ($35/liter or $125/5 liter)
Best Use: Canister filters and trickle filters mix with a small amount of bio-balls.

Siporax

Description: Sintered glass noodle. Glass is sintered with gas at high temperature and formed into a noodle approx 25mm diameter 30mm long with a large center hole. It is very porous also having perfectly sized areas for bacteria to colonise.
Surface Area: Large, approx 210m2 per liter of media.
Advantages: Does not clog. Excellent in trickle filters, – has very good gas exchange.
Excellent in sump or canister filters. May reduce nitrates in slow flow sump areas. Small amount of media required.
Disadvantages: Medium / High Cost, breaks easily if dropped (doesn’t effect performance)
Cost: Medium / High Cost ($25-35/ liter depending on amount and type purchased)
Best Use: All round good media, excellent in trickle filters and sumps.

Hagen Biomax

Description: Ceramic Noodle, a little like Siporax, but not as finely porous.
Surface Area: Large approx 1350m2 per liter of media.
Advantages: Small amount of media required. Does not clog very easily. May reduce nitrates in slow flow sump areas.
Disadvantages: Slowly clogs over long period. Breaks if dropped (doesn’t effect performance).
Cost: Medium / High Cost ($35-40 / liter)
Best Use: In trickle filters, sumps and canister filters, – good in Fluvals

Pumice

Description: Volcanic pumice, found at many beaches around NZ. Break the pumice up into small pieces ranging from 10mm to 25mm in size.
Surface Area: Medium approx 25m2 /liter of media
Advantages: Free, reasonable surface area.
Disadvantages: May contain heavy metals and silicates. Will need to be very thoroughly washed before use. Silicates may leach into aquarium leading to unwanted algae. Will slowly clog.
Cost: Free
Best Use: Trickle filters and Canister filters.

Seachem Matrix

Description: Processed pumice. Seachem has taken pumice, broken it up, smoothed the edges and washed it. It is guaranteed free from heavy metals and silicates.
Surface Area: Same as pumice above
Advantages: Ready to use, reasonable surface area
Disadvantages: Expensive, will slowly clog.
Cost: Expensive
Best Use: Trickle filters and Canister filters.

Gravel:

Description: Hard stone, non-leaching aquarium gravel.
Surface Area: Low
Advantages: Very Cheap (sometimes free). Does not clog easily, and can be cleaned
Disadvantages: Lots required, very heavy.
Cost: Very Cheap / Free
Best Use: Undergravel Filter Only

Filter Wool

Description: Dacron type filter wool.
Surface Area: Low due to being mainly air.
Advantages: Relatively cheap, very light.
Disadvantages: Clogs quickly, bacteria form about when the media is starting to clog.
Cost: Cheap
Best Use: Corner filters
Chemical filtration is the direct removal of dissolved compounds by adsorption. The most important function of chemical filtration is the removal of nitrogenous organic waste. This is vital, because such waste is both inhibitory to the biological filter and increases the load on the biological filter. It has a secondary function of polishing the water to give it a sparkle.

Adsorption

Please bear with this section, – it is a little technical, but gives a good insight into how chemical media works in general.

Adsorption, the binding of molecules or particles to a surface, must be distinguished from absorption, the filling of pores in a solid. The binding to the surface is usually weak and reversible. Just about anything including the fluid that dissolves or suspends the material of interest is bound, but compounds with color and those that have taste or odor tend to bind strongly. Compounds that contain chromogenic groups (atomic arrangements that vibrate at frequencies in the visible spectrum) very often are strongly adsorbed on activated carbon. Decolourisation can be wonderfully efficient by adsorption and with negligible loss of other materials.

The most common industrial adsorbents are activated carbon, silica gel, and alumina, because they present enormous surface areas per unit weight. Activated carbon is produced by roasting organic material to decompose it to granules of carbon – coconut shell, wood, and bone are common sources. Silica gel is a matrix of hydrated silicon dioxide. Alumina is mined or precipitated aluminum oxide and hydroxide. Although activated carbon is a magnificent material for adsorption, its black color persists and adds a grey tinge if even trace amounts are left after treatment; however filter materials with fine pores remove carbon quite well.

A surface already heavily contaminated by adsorbates is not likely to have much capacity for additional binding. Freshly prepared activated carbon has a clean surface. Charcoal made from roasting wood differs from activated carbon in that its surface is contaminated by other products, but further heating will drive off these compounds to produce a surface with high adsorptive capacity. Although the carbon atoms and linked carbons are most important for adsorption, the mineral structure contributes to shape and to mechanical strength. Spent activated carbon is regenerated by roasting, but the thermal expansion and contraction eventually disintegrate the structure so some carbon is lost or oxidized.

Temperature effects on adsorption are profound, and measurements are usually at a constant temperature.

Types of Media

Activated Carbon

The most familiar chemical adsorbent is activated carbon. Activated carbon should be a little larger than pinhead in size. When washed and dry, it should be dull and not shiny. When placed in water, it should hiss. It should also tend to float at first. Be careful of charcoal, however, because it is dull and floats, but does not hiss. Charcoal is usually very soft, crumbling easily between the fingers and is usually available only in pea-size. Good activated carbon is hard but fragile, feels hard and does not crumble, but fractures under finger pressure. Not all true activated carbons are equivalent. The most common available carbons are economical water purification grades, usually derived from wood or nutshells. These are not bad carbons, but you may wish to seek out some better grades. The best carbons are usually produced from bituminous coal and have high porosity and low density. They should also have low ash content to minimize impact on pH. Most activated carbons need to be thoroughly washed prior to use. Because it is soft it has a tendency to crush a little during shipping and is therefore covered it carbon dust. Rinse in clean before use. All activated carbons release phosphate, despite claims to the contrary, and only those that release the least should be selected for marine aquaria.

Activated carbon adsorbs a small quantity of ammonia, nitrite and nitrate, but the quantity is quite small. In most aquariums it would take a large bucket of activated carbon to remove enough nitrate to be effective. Its main use is to adsorb organic compounds. These compounds give the water its aged look (yellow). It adsorbs dissolved food, fat, and minute dirt particles.
Advantages: Easy to use, Relatively Cheap, quickly polishes the aquarium water.
Disadvantages: Must be cleaned before use, has a short life (approx. 1 month), many carbons tend to release the waste products back into the water once saturated, does not specifically target unwanted compounds (often removes fertilisers from planted tanks), releases phosphates into the tanks water when first introduced.

Zeolite

Zeolites are white, dusty clays, usually sold for removing ammonia from freshwater. They are ineffective in seawater or even freshwater that contains modest amounts of salt. Zeolites are ineffective for removing nitrates. It is often sold in boxes or bags specifically designed for use in aquariums. However, it is quite expensive considering how long it is effective for.
Zeolite really only needs to be used when setting up a new aquarium, and then only as a precautionary measure. It is also useful to have a box of it handy just in case you get an ammonia spike in an established tank. It must also be washed prior to use to remove the white dust covering it. Failure to do so will result in a rather cloudy aquarium for a while.
Some brands of Kitty litter are zeolite based. The granule size is not perfect for use in aquarium filters however, and it is also very dusty.
Advantages: Quickly removes ammonia from tanks with an ammonia spike, useful when setting up a new tank.
Disadvantages: Quite expensive, does not last long (about 1 month), must be thoroughly washed prior to use.

Aluminum Oxide

Aluminum oxide is used to remove phosphates and silicates from the aquarium water. Excess phosphate in an aquarium is the primary cause of most algae outbreaks (combined with nitrates). Can be used in both freshwater and marine aquariums. It helps solve many of the red and brown silica algae problems in marine aquariums. It is relatively expensive, but lasts a long time. Get it in bulk as it is around one third of the price by weight.
Most food has high levels of phosphate in it. Uneaten food, decomposing plants and fish waste also contribute strongly to the build-up of phosphates. The build-up usually happens faster than the aquatic plants can remove it. Also, many tap water sources are rich in phosphates. The ideal phosphate level in aquariums should be below 0.1ppm (below the measurement level of most test kits). This will slow algae growth to a level that is easily controllable. In large cichlid aquariums huge amounts of waste are produce, – all rich in phosphate. The eating habits of large fish are also such that they munch their food up leaving small uneaten particles in the water. This is style of aquarium presents the hardest algae free challenge, either requiring very regular large water changes with phosphate free water, or large quantities of phosphate removing media.
Advantages: Quickly removes phosphates down to trace level, lasts a long time, does not leach back into the aquarium.
Disadvantages: A little pricey, must be added slowly to a large volume of water as a lot of heat is produced initially. Also requires rinsing to remove the white powder deposits from shipping.

Other Products

There are some products that mix two or more types of media together. Some examples are the Ammo-Carb type products. These have zeolite and activated carbon mixed together. They are excellent for new aquariums as a precautionary measure. They need to be washed prior to use.

Nitrazorb

An aquarium pharmaceuticals product, it specifically targets nitrate. It is also the first of the filter media listed that can be regenerated. Many of the other filter media previously listed can actually be regenerated, but the method to do it is usually well beyond the capability of the equipment we have around our homes. (E.g. To regenerate activated carbon, it must be baked at over 1000°C in the absence of air). Nitrozorb can be easily regenerated using a slat solution.
Advantages: Can be regenerated, is available in a convenient size that suits most aquariums, is relatively well priced considering it can be used multiple times.
Disadvantages: Must be regenerated, – however it is an easy task.

Purigen

This is a synthetic product that performs a similar job to activated carbon – made be Seachem. It is said to have all the advantages of activated carbon, but none of the disadvantages. It adsorbs approximately 3 times as much by volume as activated carbon, taking up much less space in the filter. It can be regenerated many times using a medium strength solution of household bleach (sodium hypochlorite). Experience with the product however has shown a tendency to adsorb some of the compound in plant fertilisers, – something Seachem claims it does not do. The effect is not a problem as purigen only needs to be used for 3-4 days to clean up a tank. It can then be removed or moved to another tank. It starts off white, and turns dark brown when full. Soaking in bleach for 24 hours makes it good as new again.
It is quite expensive, but very cheap if you look at price comparisons. A 250g bottle of purigen has about equivalent filtering capacity of a 700-800g activated carbon (depending on the brand). Purigen costs approximately $52.00 for 250g. Activated carbon is about $18.00. However, you can regenerate the purigen many times at about $0.50 each time, so:
Purigen $75.00 + 60 x $0.50+ $35.00 (bag) = $140.00 for up to 5 years supply.
Carbon $18.00 x 60 = $1080.00 for about 5 years supply based on monthly carbon changes.
Purigen is clean, and can be used straight away with only a light rinse. It does not have a container however, and you must purchase a bag from Seachem to house the purigen.
Advantages: Is cleaner the activated carbon, can be regenerated many times, required less space than activated carbon.
Disadvantages: Requires regeneration, a bag to contain the purigen must also be purchased. The initial purchase is a bit pricey, but look at how much it saves long term.

Ion Exchangers

Synthetic ion exchangers are useful in freshwater to control ionic balance, remove ammonia, nitrite, and nitrate. In marine water, ion exchangers can remove some nitrite and nitrate, but have no significant effect on ammonia. They can also help to retard ionic imbalance. But, generally, the most useful function of ion exchangers, in both fresh and marine water, is organic removal, and in this they excel.
Although not an ion exchange process, this ability of ion exchangers to remove organics is phenomenal and works in both marine and fresh water alike.
Ion exchange is best used to treat the incoming tap water if it is on insufficient quality to use unprocessed. It would be a very expensive process to continually use ion exchange to filter aquarium water.
Ion exchange resins can be regenerated, but it is a time consuming process due to the large quantity of resin required. The resins are also very expensive.
Chemical filtration is the direct removal of dissolved compounds by adsorption. The most important function of chemical filtration is the removal of nitrogenous organic waste. This is vital, because such waste is both inhibitory to the biological filter and increases the load on the biological filter. It has a secondary function of polishing the water to give it a sparkle.

Designing your own Trickle Filter

This article is intended to help you design your own trickle filter. It is based on 10+ years knowledge and experience in filter building for various different sized and styles of aquarium.

Step One – Filter Media

The first thing to do is decide on the type or types of media you want to use and what fits your budget. Refer to Aquarium Filtration Part 2 for details on media types (Aquarium World May 2001). The type of filter media directly affects the size of the filter. More expensive high-density media means a much smaller filter due to the greatly increased effective surface area.

Step Two – Physical Size of the Filter:

For a given cross-section of filter media there is an optimum flow rate:

500L / hour for 100mm x 100mm of media surface area.
- For Dense Media the depth should not exceed 150mm.
- For Loose Media the depth should not exceed 600mm.

This ensures good activity from the colonized bacteria but no risk of the bacteria being washed away.

Step Three – Filter Style:

There are 2 main styles of trickle filter, a filter tower in a sump and a self-contained trickle filter.

Filter Tower

This style is basically an open bottomed tower suspended into a sump. The advantage of this type is extra flow can be added through the filter using a circulation pump in the sump. The sump is also a great place to house extra equipment like heaters to leave the main tank free of anything that breaks up the natural look. The sump can also add a significant volume to the system.

Self Contained

This is a small tank divided into sections with the biological media in the main compartment and optional chemical media in another. The return pump or outlet is in the final stage.

Examples later in the article illustrate the filter types better.

Trickle filters have their media suspended with water trickling through them so there is a large air contact. The media is not submerged.
A Trickle filter is very good at converting ammonia to nitrite and nitrite to nitrate but will not remove nitrate.

By adding a wet section to the filter using a high-density media with a relatively slow flow, some denitrification will occur. Siporax is an excellent media for denitrification.

A Water Diffuser is required to evenly spread the flow over the entire surface of the media.

Step Four – Choose your Style from the following examples:

1. Tower Filter with High Density Media

The filter is built using 6mm glass. It has a support layer + 50mm of media (Siporax) + a 50mm gap + support layer + 50mm of media (Effisubstrate)+ a gap + diffuser area so approx 300mm tall.

2. Stand Alone Filter with High Density Media

The filter is built using 6mm glass. It has a support layer + 50mm of media (Siporax) + a 50mm gap + support layer + 50mm of media (Effisubstrate)+ a gap + diffuser area so approx 300mm tall.

3. Stand Alone Filter with Low Density Media

The filter is built using 6mm glass. It has a support layer + 400mm of media (Bio Balls) + a gap between the media + diffuser area so approx 500mm tall.

Some of the media is below the water level but most is above. If you need all the media to be above then the filter must be made taller still and the media support raised up.

Planted Tanks:

If you have CO2 injection on a planted tank the trickle filter needs to be sealed. To do so requires a seal around the top edge of the water diffuser so the CO2 cannot escape. The bottom of the tower or media area must be below the water level also. If the CO2 is trapped inside the media area it must diffuse back into the water to escape. If the media area is not sealed the turbulent water flow over the media will expel the CO2 making it difficult to get the required level in the tank.

Mechanical Filtration:

If high density media is used a prefilter of approximately 15 microns will extend it’s life by 10+ times. If no prefilter is used, place filter wool approx 50mm thick on top of the filter media. This will catch the worst of the muck. The filter wool will need changing every 2-4 weeks.

Assembly:

The filter is assembled in the same manner as making an aquarium. Extra strips of glass are required in the media chamber to create an edge for the support to sit on (glued to the side walls). The support can be made from old (or new) undergravel plates.

If a stand-alone filter is made, an extra piece of glass to set the water level (a weir) is required. A suitably sized area needs to be made for the pump. This area has to be deep enough so the pump does not suck air.

You now have the information to make your own trickle filter without having to guess the physical dimensions. For larger tanks this is a much cheaper method of filtration. It’s also a lot easier to clean than canister type filters. Its only real drawback is the size and weight.

Data Sources / Acknowledgements

Discus Health Dieter Untergasser ISBN: 0-86622-168-9
Seachem: Seagram Data Sheets
Davies Pumps: Technical Data Sheet
Spa Pumps: Technical Data Sheet
Marine Invertebrates: Martyn Haywood / Sue Wells ISBN 1-56465-139-8

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