Koi Pond – Venturi

Venturis are an effective way of getting oxygen into the water. While you can build one yourself, there are many choices that you can buy now at suppliers at reasonable price. A venturi works by compressing the flow of water, then releases it abruptly into a larger chamber which creates a vacuum.  Air is introduced at the point of release, getting sucked into the stream of water creating the bubble effect at the end of the pipe.

Why aerate?

Aeration maintains a good dissolved oxygen levels in the water as reduces algae growth as it drives nutrients, nitrogen, ammonia, and soluble phosphates – all which are food for algae – to the surface air and out of the pond.

Aeration also increases aerobic bacteria that feed on nutrients on which algae and weeds need to grow, thus limiting the proliferation of algae when food supply is low. Aerobic bacteria will also eat organic sediment at the bottom of the pond. Over the winter months, aeration de-ices a winter pond because moving water won\’t freeze.

It is at this point of release that you will have to take special care when constructing your own venturi. The nozzle should reduce the inside diameter of the pipe by 50%. Fit the T-junction near the waterline, because the deeper it is, the more pressure needed and less air will be sucked in.

Test your construction before you glue the bits together. You don’t even need to glue anything else other than the nozzle so that you can make adjustments and maintenance/cleaning, unless of course if you’re setting the venture outside the pond (not submerging it) then you will need to glue everything together.

Cut, sand, and shape the PVC parts as according to the image above.

You can add a muffler for the venturi as they can get quite noisy if you use smaller diameter tubing. You can do this by drilling a few holes through a spice jar lid (one for the air pipe to the venturi, and several smaller holes for the air to enter the jar, then stuff the jar with some filter material. Spray paint the whole thing to camouflage it.

Use PVC plastic that is rated for potable water. Do not use brass natural gas fitting or any copper tubing as the nozzle because this will expose unwanted chemicals into the pond system.