AQUARIUM FILTRATION Part 2

In Filtration Part 1 all the main filter types were explained with advantages / disadvantages and relative costs. We now move on to filter media, specifically biological. Part 3 will look at chemical media.

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

To read more about the biological conversion of ammonia read this page,

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 off 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

Data Sources / Acknowledgements

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

Part 3