Below is a brief article to act as a starting place for tonight's (7/18) chat at 7pm CDT. Please, no questions on this thread until after the chat session.
Mechanical Filtration
(Prepared for Koiphen.com 7/18 chat)
As most know, there are 2 basic types of filtration, mechanical and biological. There are many approaches to both of these very necessary forms of filtration. We will attempt to limit our discussion to the mechanical side of the equation but is is important to understand first that Mechanical filtration will help our biological filtration perform better by removing solids that will otherwise hamper or biofilters’ abilities to perform at their peak efficiencies.
As stated above, mechanical filtration is the removal of solids from the water column. The two primary ways to accomplish this is through 1) separation and 2) trapping of these solids. In either case it becomes imperative to actually “remove” the solids from the system once separated or trapped. Although both of these methods work, separation is preferable to trapping of the solids. Separation allows the solids not to interfere with the movement of the water through the system while trapping collects the waste while the water is still being forced through it. Fine matting, bead filters and such are examples of methods to trap solids while vortexes, sump pits and mechanical screens (when positioned properly) are examples of separation systems.
Before we get further into mechanical filtration, its also important to understand the types of solids and their properties inorder to more fully understand why some mechanical filters are better than others and what types are more effective in varying installations.
The movement of solids through our ponds and filtration systems is dictated by a number of factors, most importantly, the solids relative buoyancies. Think of buoyancies as Negatively buoyant (sinking solids), Nuetrally buoyant (stay in suspension) and positively buoyant (float). Now, please remember that although under normal conditions negatively buoyant solids sink and positively buoyant solids float but are ponds are NOT normal conditions. Currents from returns, bottom drains and skimmers all effect the movement of solids as well and floating solids can and are pulled downward as well as sinking solids being pulled upward depending on the forces applied on the relative buoyancy of a given solid (infinitely variable).
For sake or ease, we will assume solids are collected in 3 possible locations…..bottom drains, mid-level pickups and skimmers, each targeting a specific type of buoyancy for delivery to the mechanical filter for collection and ultimate removal.
Now there are two fundamental methods of mechanical filtration, passive and active. Passive mechanical filtration would allow for a solids buoyancy to separate it from the water column for removal…..sink to a collection point, or float to a collection point. This is done by reducing the force being applied on the solid and let it fall or rise from suspension…..with the idea that the forces in the pond kept these solids in suspension to move them to the mechanical filtration to begin with. The reduction in this force is typically the reduction in the current strength that is holding those solids in suspension. A settling chamber and or vortex is an example of this method of passive mechanical filtration. Peter Waddington who made the vortex common place in the Koi hobby once thought that this method of mechanical filtration accounted for 80% of the solids in our systems. Peter eventually discovered that his estimation was a tad off too. Another person once claimed that her 400 gallon farm tank separated solids down to the 80 micron level. Well, considering the variable buoyancies, both positive and negative along with the neutrals, this is a physical impossibility! Thus a few years back, micro screens became readily available to the Koi hobby…even though that have actually existed for years. Peter quickly figured out that the vortex was NOT separating as large of a percentage of solids from the system as he once thought.
The micro screen is an example of an “active” separation system that physically separates all particulates down to the given screen size.
By removing these solids from the system, they will not have the opportunity to collect on the surface area of our biological filters, thus allowing them to be more efficient.
But a word of caution. As I attempt to communicate to all ponders, you have to design an entire system to work in conjunction with each other. Simply having the best of this, may and often times does, negate the best of another component piece. The pond, its delivery system, mechanical filtration, biological filtration must all work together to get the best synergistic effects.
Steve Childers