Using Gravel in the Pond
Should you use gravel in your pond? “Absolutely Not!” is what some of the hardcore Koi people will tell you… but we are big fans of gravel.
I originally had softball sized rocks on the bottom of my 6,000 gallon pond but had a bit of a problem with too much crud building up under the rocks creating water quality problems. Several years ago I removed the rocks on the bottom and replaced with gravel. Wow – big difference. No longer did debris build up but instead was swept away through the filters.
Above is a video “Pond Myth #14” from Platinum Ponds in Greenville, South Carolina discussing the virtues of gravel.
Below is a discussion of gravel from Aquascape:
Gravel and the Ecosystem
Over the years, ponds have been constructed with a variety of materials. Some are made out of concrete, while others use pre-form shapes or exposed liner. One of the main reasons we advise the use of gravel is because it plays an all-important role by providing a natural habitat for beneficial microorganisms. It’s also a cost-effective way to cover the liner and enhance the ecosystem.
The rocky bottom of a pond is alive and brimming with activity, covered in algae, microscopic invertebrates, and bacteria. This section of the pond is basically a compost pile. When organic debris falls to the pond’s bottom, it’s broken down by the benthic (bottom) inhabitants. These organic recyclers live off of uneaten fish food, decaying plant matter, and nitrogenous fish wastes. If this substrate wasn’t present, the pond would quickly die, effectively being suffocated by toxic fish waste and organic build-up.
Fortunately, nature has given us a way to solve this problem. Organisms have evolved to use practically every bit of available food. Fish, crustaceans, and aquatic insects will feed on these minute organisms, including bacteria and algae that live on the rocky pond floor.
In addition, gravel lends structural stability to the pond. To achieve this, gravel is placed in between and behind the boulders. This eliminates spaces between them, which keeps them from shifting around. The gravel becomes a free-floating mortar, naturally locking the boulders into place. If you’ve ever dismantled a pond that’s been build this way, you’ve experienced having to literally pry rocks out of their position.
When adding gravel to your pond and waterfall projects, be sure to vary the size of the gravel in order to provide a more natural appearance. You can have your gravel mixed at the stone yard, incorporating a blend of 3/8” to 3” gravel. The larger pieces give mass to the gravel bed, and act as a nice transition to the larger boulders. The smaller sizes provide lots of surface area, which is key for the pond’s biological activity.
Posted on: Wednesday, February 23rd, 2011 at 1:00 pm 
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Kudos to the eye-opening and informative post. It will be nice to tell clients that gravel isn’t just for the pathways but good for the water features, particularly the ponds as well.
March 30th, 2011 at 2:12 am