Salutations and such......
I get this question from both contractors and clients alike....
What's with this giant plastic tub at the top of my waterfall? Do I really need it?
Short answer..... Yup, you do need it, and it's there to help filter the pond.
Longer answer.... These big tubs are there to house physical and biological filter elements that reduce your maintenance costs and foster a healthy biome.
The filtering waterfall box/biofalls is a great way to increase your filtering capacity of the pond. Its sole purpose is to hold media that will house billions and billions of bacteria colonies, which consume and convert nutrients that would otherwise gladly grow algae in the pond proper. The water for the pond is pumped into the tub and forced through the filter media. This is perfect habitat for the bacteria that is indigenous to your area and the supplemental bacteria products (like these) that you should be using as part of your maintenance program. (If you're not using bacteria in your watergarden, SHAME ON YOU.) The more beneficial bacteria that you have growing and reproducing in your pond, the better it will look.
Most filtering waterfalls come with planting trays that sit around the edge or completely cover the top of the unit. If they do not come standard in your kit, they are available here: (Aquascape 2500, Aquascape 6000). If the tub doesn't have a tray made especially for it, fashioning planting trays can be accomplished with clay pots or planters with many large holes drilled into them. Installing plants is ALWAYS a good idea and will increase your filtering capacity by elevendy billion times, so.... you know.... do that, ok. (PLANTS! PLANTS! PLANTS! PLANTS!)
If you are installing a disappearing falls, where there is no pond at the bottom of the waterfall, feel free to use one of the smaller weir boxes or baffled units that are easier to conceal in the landscaping. (like this)(and this)
Biofalls do increase the cost of your project as they are large, bulky and are sometimes a challenge to install. When installing any waterfall tub or weir (or skimmer for that matter), be sure to compact (or tamp down) the soil underneath the unit to limit the potential for settling and frost damage/shifting.
There will be times where the tub is too big for the site. In that case, there are plenty of compact baffled weirs that will fit your situation. The biofalls type of tub does help improve the long-term health potential of the pond.
Maintaining the biofalls is not difficult. Once a season (during the spring clean out/startup), remove and clean the filter media with a hose or pressure washer. The goopier they are, the more bacteria has grown on them, which is good.
The tubs will come with some filter pads and maybe some bags to fill with loose media. Historically, we used lava rocks in bags for the filter media (that was awful and WAY TOO Heavy). Now we have cool Matala brand pads and lightweight loose media like bioballs and such, which makes maintenance easier...and and they probably function better too. When the original media wears out, replacement media is available right here.
Link for Atlantic watergarden Cut to size rolls for all Link to Aquascape brand filter
model filterfalls brands media and bioballs
I pulled this pic from the web (I believe it's a Savio product, but I may be wrong.... meh). Anyhoo, it diagrams well the layers of filtration in a filterfalls. Drop them in the tub, let the water flow through the media and seed your pond with the beneficial bacteria to get you going in the right direction.
In closing, these filter-type waterfall boxes are beneficial. Their cost is offset by the utility of added filtration.
Once again, If you have any questions about this topic, or any other, please comment and I'll get right back to you.
Thanks for reading!