Best Practices | Prefiltration System for Tortoise Pond

Published on June 30, 2021

This dude is headed for a dip.

I’ve had calls in the past about turtles and turtle ponds, and I always try my best to advise people on any related construction needs.

But I have to say that desert tortoises are a little different. A rule of thumb is that ponds built near a tortoise habitat should be raised or securely fenced off with a separate water supply for the tortoises. The Desert Tortoise Society has specific rules for water features dedicated to these animals, because they do like water and can drown easily. Several years ago, I pulled my father’s desert tortoise off the bottom of his pond twice. He recovered each time over a day or so, but he had a tendency to try to drink near the pond edge and then end up sliding in with no way out.

Big Kahunas

Last year, a client invited me to look at a local tortoise habitat. He needed help finding a solution for the poor water quality and high maintenance of the tortoise water feature. When I arrived, I was surprised to find five African Sulcata tortoises averaging what looked to be about 300 pounds each. They had a large grass area and a covered habitat along with a water feature that they routinely cruised through. The feature was a large rectangle about 15 by 20 feet. It was a concrete structure that tapered from zero along the front edge to about 5 inches deep near the back. It was surrounded on three sides by a short concrete wall with a stacked 4-by-4-foot wooden wall on top of that. Maintenance consisted of constantly draining and filling it with a submersible pump and scooping out the large, avocado-sized poop balls that were dissolving in the water.

This was going to be a challenge because breaching the concrete for drains and circulation was not much of an option. I did not need much in the form of biofiltration — mostly just prefiltration and aeration. The entire hardscape around the backside was concrete, which eliminated any gravity-flow prefiltration, so I decided to build a Static Suction Prefilter (SSP) and provide direct suction before the pump. The hard part was getting the water out of the pond with only about 5 inches of depth to work with along the back edge. I also needed to pull water from more than one point along the back edge.

SSP Construction

What I created was a 3-inch pipe assembly with adjustable slide valves opening just above the floor. I used a combination of 3-inch pipe, 3-inch coupler material and pieces of 4-inch pipe. Normally a 3-inch coupler slides just inside a piece of 4-inch pipe, so I machined the 4-incher a little larger on the inside and cut sections to act as guides. I cut an offset “L” shape in the ends of 3-inch couplers to make it a longer section when bonded together. I also molded a handle connector to fit the slide section. They form three rotating valves that can be adjusted to regulate the flow, with one at each end and one in the center. The entire suction assembly lays against the back wall just below water level with a cap on one end and a sweep 90 coming out and over the concrete edge on the other.

I needed to bore angled holes through the lower edge of the wooden wall, which turned out to be quite an effort. Whatever the wood they used to build the wall was very sturdy, but eventually the hole went through. Once outside the wall, I immediately connected the 3-inch to a 4-inch inline check valve to minimize any restriction (mostly due to those avocado-sized droppings). After the check valve, the pipe is reduced back down to 3-inch, where it is connected to a 3-by-3-by-3, three-way Pentair valve as it enters the prefilter.

My SSP is normally 2 1/2-in. on the inlet and drain, but for this project, I modified the inlet to 3-inch. (I just may make them all this way in the future!) I also made the discharge outlet 3-inch to prevent any discharge clogging when servicing. The 3-inch, three-way valve on the inlet to the tank allows you to divert water directly to the pump, bypassing the prefilter for backflushing. A W. Lim Wave I 1/6 Hp pump at approximately 4,000 gph is used to pull water through the prefilter from the pond.

The system works well, with my only issue being depth — or lack of it, allowing some air to get sucked in and occasionally starving the pump. With a shallow system like this one, maintaining the water level as high as possible is critical.

The pump pulls water from the prefilter, sending it to a 2-inch, three-way valve that allows for the diversion of pond water entering the tank from the top. This water passes through spray heads blasting the media from the top down for the backwashing cycle. In normal operation, the water travels through the three-way directly to a 4-inch diameter, 86-watt Flow Free UV light. From the far end of the UV light assembly, the water goes up over the concrete edge and down into the closest corner of the shallow area of the pond through a 1 1/2-in. pipe.

Their dedicated drinking trough is fully assembled, cue the tortoises.

Another outlet goes out the end of the UV light assembly to a wye, which serves as a cleanout, and another 1 ½-inch water pipe that runs under the ground to the far corner of the shallow area. Each of the ends of the returns at the shallow end has a spray head assembly that fans the water out in a 90-degree pie shape into each corner of the pond, much like a 90-degree sprinkler head sprays the corner of a section of grass. This head is upside down against the concrete and fans out immediately. The fan of water is my source for oxygen, much like a waterfall is for a garden pond. The existing auto-fill was modified with a tee assembly that holds both the float and a ¾-inch valve to allow for faster filling when necessary.

Water Works

The system works well, with my only issue being depth — or lack of it, allowing some air to get sucked in and occasionally starving the pump. With a shallow system like this one, maintaining the water level as high as possible is critical. The auto-fill timer has been adjusted multiple times to add enough water to keep up with the abnormal evaporation in a shallow system like this.

Tubular valves are spaced and laid out before installation.

The filter area was enclosed with a lot of ventilation in the roof because of our intense Las Vegas heat. The system has taken some tweaking but has eliminated the weekly draining. The large tortoise turds are scooped out on occasion and, if they get pulled in, can travel easily into the prefilter and be flushed out when necessary.

Ninja Tortoises

Toward the end of the project, the client decided he wanted a drinking trough along the back wall of the building next to the pond to give the tortoises another option for drinking water. The tortoises regularly cruise through the feature but do not appear to drink out of it. Their other options are water jugs standing in several places in the yard, but these regularly get plowed over when the boys start to wrestle, so this gives them another source. The trough is a split section of 6-inch pipe with inlets and outlets on the ends. The water is connected to the system through the cleanout protruding from the end of the UV light. Water is diverted to the far end of the trough and spills back in near the corner.

It was a fun and interesting project with a set of challenges not normally found in the pond world. It was also a learning experience. For instance, I learned that you don’t really know what a real head-butt is until you get one from a 300-pound tortoise wanting to know where his water went!

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