Most pet fish live in either an indoor tank or outdoor pond. What should the bottom of your tank look like? What should the bottom of your pond look like? Ponds are much more flexible than tanks; they can have a lot of different shapes, layouts, and “all natural” finishes. What is the “healthiest” bottom for your pond is essentially the easiest to clean = nothing.
The substrate material lining the bottom of your garden pond plays an important role in maintaining water quality and ecosystem balance. Selecting the right type of bottom cover will help create a healthy environment for fish, plants, and other aquatic life. There are several options to consider when deciding what to place on the bottom of a garden pond.
Bare Pond Bottom
A bare pond bottom has no substrate covering the liner or concrete base. This option is easy to clean with a pond vacuum, allowing you to remove debris and prevent accumulation of organic waste However, a bare bottom provides no surfaces for beneficial bacteria to colonize These bacteria help break down fish waste and other nutrients. A bare liner also offers no protection from UV rays which can degrade the liner over time.
Sand
Fine sand provides a natural look and feels pleasant underfoot for wading ponds. Sand easily shifts and settles requiring occasional raking to prevent heavy buildup or compaction in some areas. Sand particles can clog pumps and filters. Sand offers minimal spaces for helpful bacteria to grow. Unless a special coating is applied, plain sand provides little UV protection for the liner.
Pea Gravel
Smooth pea gravel around 1/4-1/2 inch in diameter makes an attractive pond bottom cover. The small stones don’t obstruct water flow or big frequency to colonize. Yet large enough not to enter pumps or clog filters. Pea gravel settles relatively little and is easy to vacuum. Use multiple pounds per square foot to provide a stable base and adequate bacterial habitat.
Small River Rock
For a natural stone appearance, small rounded river rocks 1-2 inches across create an aesthetically pleasing pond bottom. Gaps between the stones allow water flow and debris to settle between rocks. Vacuuming takes more effort, needing to stir up debris. Use a thicker layer of at least 2-3 inches for stability. Smaller rocks will get drawn into pumps.
Large River Rocks
Bigger river rocks over 2 inches across provide large crevices for healthy bacterial populations. The heavier rocks stay put better than smaller gravel. Vacuuming around large rocks is difficult. A thick 3-4 inch minimum layer prevents compaction. Use very rounded rocks to avoid liner damage. Keep rocks away from pump intakes which can jam.
Blended River Rock
A mix of small and large river rocks combines the benefits of the different sizes. The small rocks fill the gaps between larger stones to inhibit debris accumulation while allowing water flow. A 3-4 inch blended mix prevents settling while providing bountiful surfaces for essential nitrifying bacteria. Vacuuming takes more work around the larger rocks.
Cobblestones
Flattened cobblestones offer a visually interesting and textured alternative to rounded river rocks. Their smooth faces won’t damage the liner. Use at least a 2 inch layer to avoid settling. Pond vacuums can remove debris between the gaps. Keep away from pump intakes which could clog. Add larger rocks on top to vary heights.
Crushed Quartz
Crushed quartz like Crystal Quarts provides a shimmering pond bottom that reflects light. The smooth grains won’t harm liners. Silica improves water clarity by absorbing phosphates and organic molecules. Vacuuming quartz is easy with no small particles to clog pumps. Needs at least a 2 inch layer to avoid compaction.
Bentonite Clay
Bentonite clay contains montmorillonite which absorbs nutrients, chemicals, and waste from the water. It provides a natural liner sealant. Bentonite has a high cation exchange capacity to attract and hold positively charged ions. This helps remove ammonia, heavy metals, and other contaminants from ponds.
Pond Soil/Potting Mix
Some ponds use soil, potting mix, or compost on the bottom to create a more natural environment. However, this allows heavy accumulation of organic debris, creating thick sediments lacking oxygen. Anaerobic bacteria generate toxic hydrogen sulfide gas which can harm fish. Must be vigorously stirred often to prevent this.
Best Options for Garden Ponds
For most backyard garden ponds, a 2-3 inch layer of smooth pea gravel, small river rock, or a blend provides the best combination of aesthetics, ease of cleaning, bacterial habitat, and water filtration. Avoid sand and materials with fine particles. Limit soil and organic matter. Add some larger accent rocks. Test pH balance of stone types. Keep intake areas clear. Proper substrate selection creates a healthy garden pond.
Plants/Mud/Bog/”All Natural” Pond Substrate
Pros:
Cons: Your lack of cleaning effort creates a dangerous health hazard to your fish. There are layers of bacteria that can’t get oxygen from the water because of the dense plants and trash and fish waste. These anaerobic bacteria use sulfur as a food source. Hydrogen sulfide will kill all of your fish if you mess around in the muck or if your fish try to flash on this surface.
It is impossible to recreate a native environment in a synthetic fish system. “All natural” systems in wild environments use multiple species working together to balance waste management. In a man-made pond, you are missing many of these critical elements. Do your regular maintenance!.
How do I clean my pond bottom?
The easiest way is by using a pond vacuum. These items are specially designed to make cleaning ponds easy. Think of it similarly to a pond-size gravel siphon. Use a long brush or stick to stir up the substrate every so often if you don’t have a vacuum. This will bring oxygen deep into the cracks and crevices, preventing anaerobic bacteria formation.
Use our helpful checklist to make sure you get all of your daily, weekly, monthly, and yearly tasks done on time. It has more information on how to clean a pond. Remember: water quality is the #1 influence on fish health! Regular maintenance is the best thing you can do to keep your pond healthy.
How to Build a Garden Pond (w/ Monica from The Weekender)
FAQ
Should you put anything in the bottom of a pond?
What is the best bottom for a pond?
Should you put rocks in the bottom of a pond?
How do you fill a pond with water?
Run the electrical cord up the side of the pond. Plug it into a GFCI outlet. With a good garden hose, fill the pond with water. Stop filling at two to three inches from the rim of the pond. Cover as much pond liner as possible with stonework or aquatic plants since UV rays break down liner materials.
How to build a pond?
Digging the hole is just one step for building a pond. Once you have dug the hole, you will have to smooth it out and then lay pond liner on it. The liner is important because it prevents the water from escaping through. Once you are done, you also need to think about putting something at the bottom of the pond.
Should you put gravel on a pond?
Large ponds generally have mud at the bottom, and that mud usually has a depth of several inches. By adding gravel on top, you are effectively limiting the microbial growth. The gravel also begins to mix in the substrate, which effectively reverses the benefits. If you have a smaller pond, it’s much easier to manage.
How do you protect a pond lining?
If you have built a garden around the pond, it won’t take long before the soil becomes waterlogged due to water leaking from the pond, and many of your plants will die. To protect the lining underneath, you will have to add sand or another material. This will also ensure that the pond liner remains trapped in the bottom.