Biological Filtration 201 Chapter 2
Upflow Gravity Biofilters
The next type of biological filter we’ll talk about is the Upflow Gravity Biofilter, again named for the direction of flow. Instead of water moving horizontally in Downflow Filters from one chamber to the next, filling them up one after the other and then finding its way back into the pond from a distance, water is pumped into the bottom of the Upflow Biofilters, where it leaves a good part of the sediment it carries, forcing its way upwards through a mechanical filter pad and over biological filter media before overflowing over a wide weir back down into the pond. The usual configuration is to directly attach the liner to the filter to ensure the water stays within the confines of the liner, and the filter is typically mounted at the beginning of a stream that flows back to the pond, although neither of these parameters are necessary – the filter can be set inside the liner to overflow directly into the pond, for example. These filters are very easy to plumb, very effective mechanical and biological filters and very easy to install and hide. They have almost completely supplanted the Downflow type in popularity, for one major reason – it’s harder to have a major leak that will empty the pond.
Now, please don’t misunderstand – it is ALWAYS possible to really screw up just about ANYTHING (and we have). It’s just arguably easier to keep from screwing up with the Upflow design, because it’s physically attached to the liner, instead of being located remotely. The lip of the Upflow filter is usually physically connected to the liner in such a way that all the water ends up in the pond pretty reliably, as long as there no problem with the attachment of the liner. You can read about FilterFalls liner attachment here, in the PRO INSTRUCTION BOOK.
By controlling exactly how and where water flows back to the pond, directly on top of the liner, the Downflow Filters’ issues of remote location and plumbing connections back to the pond are eliminated. There’s also less chance of the filter outflow clogging, since the overflow of the Upflow Filters is usually almost as wide as the widest part of the filter itself, where the Downflow filters are often an easily clogged 2” to 4” inch pipe. Even those that are designed with a waterfall return always locate the spillway on the narrow side of the filter. Finally, all the debris in an Upflow filter is trapped below the media, where it cannot get to the spillway, rather than the debris being able to float and overflow from chamber to chamber all the way to the outflow.
The fact that water is pumped into the bottom rather than poured into the top makes a huge difference also. Hydraulic pressure forces water through filter pads with the same inexorable power that tree roots use to crack cement, and that means water will keep flowing through filter media for an amazingly long time between cleanings. It’s not uncommon for a properly sized Upflow Biofilter to go an entire season before needing to be cleaned. When they do need to be cleaned, most of the time they can be easily flushed of the accumulated sediment in the bottom, and the pads or mats and other media quickly rinsed.
The next type of biological filter we’ll talk about is the Upflow Gravity Biofilter, again named for the direction of flow. Instead of water moving horizontally in Downflow Filters from one chamber to the next, filling them up one after the other and then finding its way back into the pond from a distance, water is pumped into the bottom of the Upflow Biofilters, where it leaves a good part of the sediment it carries, forcing its way upwards through a mechanical filter pad and over biological filter media before overflowing over a wide weir back down into the pond. The usual configuration is to directly attach the liner to the filter to ensure the water stays within the confines of the liner, and the filter is typically mounted at the beginning of a stream that flows back to the pond, although neither of these parameters are necessary – the filter can be set inside the liner to overflow directly into the pond, for example. These filters are very easy to plumb, very effective mechanical and biological filters and very easy to install and hide. They have almost completely supplanted the Downflow type in popularity, for one major reason – it’s harder to have a major leak that will empty the pond.
Now, please don’t misunderstand – it is ALWAYS possible to really screw up just about ANYTHING (and we have). It’s just arguably easier to keep from screwing up with the Upflow design, because it’s physically attached to the liner, instead of being located remotely. The lip of the Upflow filter is usually physically connected to the liner in such a way that all the water ends up in the pond pretty reliably, as long as there no problem with the attachment of the liner. You can read about FilterFalls liner attachment here, in the PRO INSTRUCTION BOOK.
By controlling exactly how and where water flows back to the pond, directly on top of the liner, the Downflow Filters’ issues of remote location and plumbing connections back to the pond are eliminated. There’s also less chance of the filter outflow clogging, since the overflow of the Upflow Filters is usually almost as wide as the widest part of the filter itself, where the Downflow filters are often an easily clogged 2” to 4” inch pipe. Even those that are designed with a waterfall return always locate the spillway on the narrow side of the filter. Finally, all the debris in an Upflow filter is trapped below the media, where it cannot get to the spillway, rather than the debris being able to float and overflow from chamber to chamber all the way to the outflow.
The fact that water is pumped into the bottom rather than poured into the top makes a huge difference also. Hydraulic pressure forces water through filter pads with the same inexorable power that tree roots use to crack cement, and that means water will keep flowing through filter media for an amazingly long time between cleanings. It’s not uncommon for a properly sized Upflow Biofilter to go an entire season before needing to be cleaned. When they do need to be cleaned, most of the time they can be easily flushed of the accumulated sediment in the bottom, and the pads or mats and other media quickly rinsed.
