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Rocks, Bottom Drains - The Debate Continues

by John Olson

Today I came across a social media debate on bare liner ponds with bottom drains and water gardens with rock sides and bottoms. This pond industry debate has been going on for several years now but in reality, both sides have some great points. Ultimately it comes down to what type of pond are you looking for? I hope this article will give you some things to consider.

Should I install a pond with a gravel bottom or a bare liner with a bottom drain?

This is another great question that only the pond owner can answer when they are designing their new pond. The gravel bottom pond has been a staple of construction for many years now. The installation of a bottom drain is not a task for the first-time builder and if installed improperly the pond will leak. However, if installed correctly, a bottom drain can be extremely beneficial both to the health of your fish as well as to the homeowner in greatly reduced maintenance.

Here are some things to consider about gravel bottoms and bottom drains when designing your pond:

  1. Like many builders I was trained to install gravel bottom water gardens (not Koi ponds) with 1-2 inches of gravel as many pond builders do. I enjoy the look but have grown concerned over the last couple of decades with some issues. Three main issues with gravel bottoms are cleaning, circulation, and dead fish.

    First, cleaning does take a considerable amount of time when you have to vac out the settled organic muck such as fish waste and decaying plant matter.

    Second, with a gravel bottom and no bottom drain you have limited circulation in the pond. A skimmer filter system will circulate only the top stratus of the water. A bottom drain, when installed properly, allows the dirty water from the bottom to be pulled out and run through a filter before discharging back to the top strata of the pond. This keeps the pond both cleaner as well as an even temp distribution allowing the fish to move from zone to zone freely which makes watching them more enjoyable. With or without a bottom drain the use of an aeration system with also aid with bottom to top circulation as well as put the beneficial bacteria colonies (housed in the biological filter) into overdrive helping keep the water clear.

    Third, unknown to many consumers as well as less experienced installers, gravel bottoms over 2 inches thick can house colonies of poisonous bacteria (not to be confused with the beneficial bacteria added to the pond to consume excess nutrients). This toxic poison grows only where there is no oxygen. The problem happens when someone disturbs this gravel layer (perhaps by using a vac or using a hand net to take out leaf debris). Those toxins can then be inadvertently released into the body of water causing fish illness or death.

  2. Its easy to envision Koi swimming around in rock filled natural pools of water in nature but one might be surprised to learn that commercial Koi across the world are bred in mud ponds and rockless liners. This ties into my next point of interest.

  3. There is an age-old dispute between the preferences and differences between Koi ponds and water gardens. Both types are substantially different. A water garden is a decorative pond filled with waterfalls, rock sides and sometimes bottoms. It is often filled with plants and may have Koi in it. This is the kind of pond that a consumer will fill with $10-$50 koi and one they can sit beside and relax to the sound of falling water. This is the type of pond that I personally enjoy. While I no longer suggest ponds with gravel bottoms, I find no harm in the use of large decorative rocks on the sides and tops for the majority of homeowners.

    On the other hand, a serious Koi pond hobbyist would never consider putting rocks in his pond. Not on the sides and certainly not on the bottom. When Koi breed, they swim erratically and throw themselves all around the pond. The last thing a Koi owner that spent 2K on their prized possession wants is to see it with lacerations or to having lost an eye due to flashing roughly against rocks. Instead, a typical Koi pond will be bare liner, with a bottom drain and massive external filters for enhanced circulation. The owners of these expensive fish want to see them perfectly with no clarity issues and definitely no rocks. This is not the type of pond that most of us build to enjoy.

  4. Of course there are many builders offering hybrid Koi ponds that incorporate extra filtration, bare bottom ponds along with some decorative rock walls and features. In the end it all depends upon the things that are most important to the pond owner during the design of the pond.

Best wishes to all for a great pond season!

John Olson – Graystone Industries
1-23-2020