Pond Bottom Drain Technology

Yesterday and Today

Sample Bottom Drain
Sample Bottom Drain

In the last decade bottom drain technology for ponds has come a long way. Yet much of the educational material available for bottom drain installation is either swimming pool technology or dated koi pond technology.

That combined with some clever marketing by an equipment manufacturer to discourage pond drain installations, it’s no wonder that contractors and homeowners still sadly misunderstand bottom drains.

Why would you want a bottom drain for your pond? The reason is simple! REDUCE MAINTENANCE. Pond drains done right remove organics from the pond and create a unique dynamic in the pond’s circulation system.

Water Garden/Eco-System ponds rely on beneficial bacteria colonies to breakdown fish waste and other organics such as leaves, pine needles, pollens, dust and all other forms of water- logged debris that typically settles on the bottom of a pond.

 Water Garden/Eco-System ponds typically rely on a shallow bed of gravel on the bottom of the pond to help manage organics because it serves as a place for beneficial bacteria to colonize. (See Figure 1.) The gravel needs to be managed regularly to avoid undesirable conditions for beneficial bacteria colonies. As a rule, this requires draining the pond each spring in order to wash and clean the gravel bed.

A dedicated koi pond, on the other hand, is completely opposite and traditionally will not have gravel in the pond. (See Figure 2.) Dedicated koi ponds rely on a bottom drain (or drains), circulation jets, aeration and pond vacuums to keep the pond free of debris. This eliminates the need to drain the pond annually for cleaning.

Only within the last decade has a bottom drain been commercially available with an air diffuser built into the unit to optimize efficiency of the bottom drain’s ability to capture solids. You can visit just about any specialty koi dealer across America and witness the change in technology first hand! Any display pond at a koi specialty facility that is older than 2003 will likely not have an aerated bottom drain!

I would be very surprised if you find a display pond at a specialty koi dealer’s establishment that is seven years or older WITH an aerated bottom drain, and would say you are at a facility that has helped pioneer aerated drains. Please spend money with them! They deserve your financial support for their efforts!

Advances in bottom drain technology are extremely exciting to our organization. It is only because of these advancements in Pond Bottom Drain Technology within the last few years that we even offer pond drain installations today.

Our construction team has offered pond drain installations since 2007 and we have made it a point to really begin educating and promoting bottom drains as part of our pond design consultations.

We help our clients determine what size bottom drain is best for their pond, show them how to determine optimal flow rates for their drains, explain how proper use of aeration complements a pond drain’s ability to remove solids and explain the fundamentals we use for designing bottom drains into koi pond systems.

Pond Drain Dos & Don’ts

We only recommend gravity flow bottom drain installations into pre-filter separation systems as opposed to direct suction drain installations. Gravity flow means we are plumbing the bottom drain to a pre-filtration unit and from the pre-filtration unit we are pulling water with an external pond pump and sending clear water to filtration. For example, the bottom drain can be plumbed to a settling chamber, a settlement tank, a sieve pre-filter or pond skimmer.

In a gravity flow installation your pre-filter will be at the same water level as your pond and by removing water from this pre-filter, the law of gravity is pulling water from the pond through the bottom drain line to fill the pre-filter. Believe it or not, it’s only in the last decade gravity fed settlement units have become commercially available as a proprietary product from pond equipment manufacturers.

Some of the construction options for gravity flow installations are more difficult to install than others. Of course the cost of gravity flowing your pond drain to a determined pre-filter varies greatly and as you can imagine, the more difficult and costly the installation, the easier the maintenance.

Whichever the case, I am not a fan of plumbing bottom drains directly to the pump and I will NOT assume the reasons are obvious. If you use direct suction pond drain technology in a koi pond, here is what you set yourself or your client up for.

Fish poop, among other things, makes its way to the direct suction drain (typically 2˝ or 2 1/2˝ PVC line) and is rapidly sent to a strainer basket in front of a pond pump. Fish poop is blended up “Margarita style,” without the ice, yummy flavor or intoxicating effect, and is sent to a pond filter in an extremely messy way.

For you pond keepers below the age of 21 we will refer to it as a Fish Poop Smoothie. The strainer basket in front of the pond pump likely needs to be opened and cleaned a minimum of once a week; however I have seen extreme cases where homeowners were cleaning their strainer basket several times a week! Because of a well-designed Gravity Flow Pre-Filtration System, by Kent Wallace of Living Water Solutions, I clean the leaf trap on my pump only TWICE A YEAR whether it needs it or not.

I’m hoping we all agree that gravity flow technology is the superior construction method over direct suction technology, so lets segway to some speed limits we need to recognize. Most ponds will require 3˝ or 4˝ bottom drains so we will only cover these pipe sizes in this exercise.

3˝ Gravity Flow Bottom Drain Installations optimally have a flow rate of approximately 1500 to 1800 gallons per hour and will service an 8´ diameter pond bottom nicely.
4˝ Gravity Flow Bottom Drain Installations optimally have a flow rate of approximately 3000 to 3600 gallons per hour and will service a 10´ diameter pond bottom nicely.

Please do not ignore these speed limits like we know you do on the freeway! If you flow water faster than these speed limits the velocity of the water will begin to break up solids such as fish poop defeating one of our main purposes and on the flip side, if you flow too little water, you aren’t removing solids from the pond in the most effective manner possible.

The service diameter of the gravity flow bottom drain can be enhanced greatly by a bowled excavation with the drain installed at the lowest point of the pond and current jets flowing water in a circular pattern around the pond drain. Additionally, you can increase the area of influence around the bottom drain by the induction of air just above the anti-vortex cover. Air drains are the most recent innovation readily available from koi specialty part manufacturers.

Current jets can be designed in the pond to create a slow vortex, spinning solids to the bottom and heavy aeration from the top of the bottom drain actually pulls neutrally buoyant solids (like fish poop) directly into the suction of the Gravity Flow Bottom Drain. I would say with these additions to a pond drain installation, IF YOU WANTED TO PUSH THE LIMITS, you could extend the service diameter of a 3˝ bottom drain to 12´ and a 4˝ bottom to 14´.

Use these Bottom Drain Fundamentals that we use to professionally design koi ponds each day. Keep in mind that the length and width of your pond will determine the recommended size & quantity of bottom drains. The number of drains (combined with total pond gallons and number of skimmers) will help us determine what size pond pump is necessary for the life support system of the pond.

I was never a wiz in History back in school but we sure can learn a lot about pond construction by keeping a watchful eye on techniques and philosophies used over the years. The Bottom Drain philosophies of today are certainly on the rise and I predict could become mainstream in the industry as a standard item in all new pond construction, water gardens, eco-systems and dedicated koi ponds alike.

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