What are Filter Media, and how do they work?
by: Demi Fortuna
Here's the problem: the better something filters, the more maintenance it usually requires. However, the more maintenance a filter needs, the less it's likely to get over time, as folks get sick and tired of cleaning it. Manufacturers have created filter media to deal with this conflict in three different ways.
Filter Matting and Foam Pads – This is the 'Clean It Often' type or, as I sometimes think of it, the 'Gone With The Wind' approach, as in: "Frankly, Scarlet, I don't give a damn… how often you have to clean your filter". Filter Matting and Foam Pads, like the ones found in Submersible Filters, are inexpensive and work great to start with, but they clog relatively quickly, need pressure (usually a jet of chlorinated hosewater) to dislodge trapped debris and don't clean completely. They are cheap and effective but require messy cleaning that kills beneficial bacteria or frequent replacement, so they're best used in small ponds as first filters or for stay-at-home homeowners who can clean them as needed. Danner PM1000 Prefilters are a good example of this type.
Particulate filter media and BioBalls – The 'Less is More' strategy. If you want to go longer between cleanings, use Particulate filter media or BioBalls that don't trap all the particles, at least not right away. That is, if there's plenty of space for aerated water to get between media with lots of surface area, the filter will grow lots of beneficial bacteria and go a long time between cleanings. Many Pressurized Filters are designed this way. The spaces between the media ("interstitial spaces") are relatively large so debris flows right through them at first; they don't filter well to start with but the free flow of aerated water through the media encourages a growth of beneficial bacteria. It takes 4-6 weeks for bacterial colonies to fully develop, and that's when the filter starts to work. As the colonies grow, they cover the media with a sticky biofilm, to which more and more particles get stuck. As debris starts to build up and close the spaces between media, the filter removes smaller and smaller particles, filtering better and better as the media clog more and more. Finally, when totally clogged, which can take weeks or months, filters with this type of media backwash easily, reinvigorating bacterial colonies by sloughing off debris and exposing fresh 'bugs'. So, Pressurized Filters with Particulate filter media take a while to start up, but filter biologically very well and eventually also filter mechanically well. They should be backwashed only when needed, as they work best when partially clogged. See Tarpon 40 Pressurized Filters
Matala mat – The 'More is Better' solution. The more surface area, the longer media take to clog, and the longer between cleanings. Matala mat has lots of surface area, large "interstitial spaces" (and you thought you'd never see that word again) combined with a semi rigid structure that makes it easy to rinse clean in a bucket of pondwater without damaging bacterial colonies. Now, there are lots of ways to increase surface area... One 'industry giant' simply super-sized whole filters, literally to the size of Jacuzzis in which small ponies could comfortably bathe, but those required Herculean labors to clean. Other manufacturers use media jam-packed with lots more surface area per square foot (so called Specific Surface Area, or SSA), but this microscopically manipulated media can clog easily and be very expensive. The easiest way to increase the surface area of the media in a generously sized filter, such as the External Filter, is simply to stack lots of Matala mat in the filter. Take a look at this Matala mat kit. External Filter Atlantic Water Gardens BF2600
Properly graded Matala mat stacked coarse on the bottom, medium then fine on top easily doubles these filters' surface area and effectiveness both biologically and mechanically, while remaining relatively clog-free and easy to clean.