Bio Filtration Options
Like the mechanical, I'll separate the biofiltration options into two categories - open or closed. An open system just means that it is open to the air. You can gravity flow an open system or pump feed it. It's very flexible in the plumbing design and media used. A closed system or a pressurized system is completely contained and must be pump fed. It is the simplest to install.
Open systems are generally preferred for biofiltration. In addition to the flexability advantage that gravity feed allows, open systems allow contact with the surrounding air which is critical to biofiltration. In closed systems, oxygen must be taken from the water column.
Closed systems Pressurized filters
There are many pressurized bio filters available. They are all similar in concept but differ in two ways - the internal plumbing of the filter and the media they use. The fewer turns and bends in the internal plumbing and the larger the plumbing, the better. All pressurized bio filters add head to your system and need to be pump fed. However, less restriction and larger plumbing will lower the total head of the system and the pump won't have to work as hard. Typically a pressurized bio filters will add about 10' of head to a system.
There are two basic types of media - beads and open cell media. Examples of bead filters include GC Tek's AquaBead, Sac Koi's Challenger, AquaDyne. The small bead offer a great amount of bio surface for the filter and they pack tightly together so function very very well as a mechanical filter. However, because it's so effective at trapping debris, the filter needs to be backwashed/cleaned often. If not the filter clogs quickly and the trapped debris may start to decay. Everytime the filter is backwashed that bio film that has been built up is disturbed and the bio filtration capability of that system is decreased.
Pressurized bio filters with open cell media inculde Aqua's Ultima, WLim's BioWave. These filter use open cell media like K1 that have voids within the media. These voids give the bacteria a semi protected environment to grow and therefore can be more effective in bio filtration. When the filter is backwashed not as much of the bio film is wiped out because of these protective environments. However, since the media is much larger they do not function as well in terms of mechanical filtration. The downside of all pressurized bio filters, regarless of the media, is that they need to take oxygen from the water column in order to do the bioconversion.
Summary- Pros
- Easy to plumb
- Bead Filters
- Great mechanical filtration
- The small beads used in these filters provide a large amount of surface area for bio filtration
- Pressurized Biofilter
- Very good mechanical filtration
- Voids help protect the bio film in the backwash process
- Cons
- Adds significant head pressure to the system
- Frequent backwashing is necessary for maintenance
- If not maintained well, even more head pressure will be added to the system
- In badly maintained cases trapped debris can start to decay.
- Backwashing disturbs the biofilm and knocks down the bio filtration function.
- Effective backwashing often requires an additional blower
- Must be pump fed
- Removes oxygen from the water column
- Expensive
- Approximate cost: they start at around $1200; the bigger they are, the more expensive it gets and they can get every expensive.
- DIY factor: medium/hard. If you're looking for one of the bigger bead filters, you can save quite a bit of money if you DIY. You would start with an empty sand filter body for about $200-$300, buy your own beads and make your own internal laterals.
Open systems Submerged bio filtration
Submerged bio filtration is probably the most common type of bio filter. The skippy filter is an example of a submerged biofilter. Japanese Mat or JMat is also very popular as submerged bio media. The media can be pretty much whatever you want - hair curlers, pot scubbers, bird netting, etc. The more surface area the better. Even gravel or lava rock will work but these options are much more difficult to clean because of their wieght. Submerged bio filters can be run upflow or downflow. Regardless of the media choosen or the direction of the flow, aerating it will help biofiltration by providing an oxygen rich environment for the bacteria to act in.
Summary- Pros
- Very easy to DIY
- Almost anything can be used as media.
- Almost anything can be used as a containter.
- Cons
- Needs to be maintained/cleaned which can often be messy
- Cleaning disturbs the biofilm and knocks down some of the biofiltration effectiveness
- Approximate cost: Cheap, cheap, cheap. Since the media can be pretty much anything, use whatever you have that's lying around.
- DIY factor: easy
Moving bed filters
A moving bed filter is like a submerged filter except the media is neutrally bouyant or close to neutrally bouyant and it is very heavily aerated. Fluidized beds generally use open cell media like kaldness. Kaldness type media is especially effective because the little protrusions on the end of the media help the media tumble and churn. The heavily aeration constantly moves the media and the constant bumping/churning of the media rubs off dead bacteria allowing the filter to be "self-cleaning". Lastly, the oxygen saturated environment allows for very effective bio converstion
Summary- Pros
- Very effective bio filter
- Aeration is part of the system
- "Self-cleaning"
- Easy to DIY
- Cons
- Cost
- Requires an air pump
- Approximate cost: Media is about $25-$40/cubic foot
- DIY factor: easy/medium
Wet/Dry Filters - Trickle towers or Shower filters
In these wet/dry filters, water enter the top of the filter thru either spray bars or a drip plate. I doesn't really matter what you use. The idea is to evenly distribute the water over the media. The water then flows over media which is exposed to open air. Since the media is not submerged so you get maximum air exchange. Also it allow for other gases trapped in the water such as carbon dioxide to escape. Finally the falling water, washes away debris and dead bacteria on all the upper parts of the filter so this acts as a self-cleaning filter as well. The sump, which is the last tier of the filter, is the only part that needs to be cleaned.
The main difference between a trickle tower and a shower is the volume of water. Showers have a much higher volume of water so the degassing effect is great as the water crashes over the media instead of slowing cascading as a trickle tower would. The other difference is that shower filters normally have multiple trays or tier. This is so that the water can crash into each tray promoting degassing and air exchange.
There is a commercial product called a Bakki Shower. The trays are made out of stainless steel. The media used in them is Bacteria House. Bacteria House is just a porous ceramic media with a lot of surface area and since it's made out of ceramic it will not really break down over time. However, virtually any media with high surface area can be used. Lava rock is a very option since it is cheap and readily available. Since this is a self cleaning filter, the weight of the rock is not an issue as long as it's not in the sump area.
Summary- Pros
- probably the most efficient bio filtration option
- cheap and easy to DIY
- self cleaning
- self aerating
- Cons
- may be noisy
- will increase evaporation
- can decrease overall pond temperature
- DIY factor: easy. Anything UV resistant can be used as a container.
- Approximate cost. Can be done very cheaply with milk crates and lava rock
01-31-2008
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