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sternotherus odoratus sponge filter basket setup underbed storage box

Attempting to create a sponge filter system for
Sternotherus odoratus


Common musk turtles, or stinkpots (Sternotherus odoratus) are a small species of North American turtle, which naturally inhabit slow moving, sluggish backwaters, or still ponds. After a couple of years experimenting with sponge filtration in fish tanks, I decided to try and replicate a similar, stillwater setup, for two adult female musks.


How does it work?

The concept is relatively simple; a low wattage pump pushes air to the bottom of the water through silicone tubing, and creates bubbles as the air passes into the water through an airstone. As the bubbles rise to the surface through a series of submerged sponges, they create a tiny current, pulling water through the sponges as they go. These sponges act as a growing medium for millions of bacteria, which clean the water which passes over them, acting as a form of biological filtration.

Biological filtration is relatively ignored by turtle keepers, mainly because turtles are not as sensitive as fish, and can handle ammonia and nitrite spikes that would leave many fish seriously ill. The main method of filtration in turtle tanks tends to be physical/mechanical filtration, where a filter pushes water through sponges to trap debris and waste, keeping the water clear and making it easier to clean.

Something doesn't sit right with me about this however. Sternotherus in particular come from water sources with large amounts of organic debris - fallen leaves, algae growth, branches etc. They are adapted to scavenge on the river bed, or pond floor, amongst this debris, posessing small barbels on their chins which act as sensory organs. Whilst sparkling clear water looks good to us, it doesn't seem to be what this species is used to.

So, from this, I set about creating an enclosure for these two adult females, using an air-driven sponge filter, similar to those I use for fish. The idea being that regardless of organic debris on the floor of the enclosure, the water quality would stay safe and clean, even if it didn't appear so.

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The enclosure this filter was made for is an underbed storage box, with a similar footprint to a 60G aquarium. Full details about this enclosure can be read here.

The filter itself was made from a pond planting basket. The first photograph shows it roughly in place in the corner of the enclosure, with the airstone connected up, to give an idea of the concept. This basket filter also doubled up as a basking area, which can be seen in the later photos.

The first step was to attach the airline tubing and airstone to the bottom middle of the basket using a cable tie, to prevent it moving around under the sponges (photograph 2). After this, I used a mixture of sponges to fill the basket 3/4 of the way full. These sponges were mainly bath sponges, sold in supermarkets and chemists. The sponges were soaked in clean water for a week to ensure there were no residual chemicals from packing. Some of these bath sponges were also placed inside my Red Eared Slider filter for a week, before being placed in the basket, to allow bacteria from my Slider's established filter to colonise them and kick-start the cycling process.

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Once the sponges were in, they needed to be weighed down to prevent them floating as air was pumped through them. This was achieved using platic mesh (in this case, "gutter guard" sold to stop leaves clogging up drain pipes - photo 4) and a layer of pre-soaked expanded clay pebbles (or "hydrolecca", used in hydroponics) ontop (photo 5). These pebbles should also act as another surface for the good bacteria in the filter to colonise.

Once the sponge and hydrolecca filter medias were in place, I began constructing the basking area, using driftwood collected from a local beach. After a good scrub in hot water, I placed the main piece as I wished (photo 6), and marked two sites on the back where it touched the basket using a pencil, to allow me to drill holes and cable tie them together. This helped keep the driftwood in place.

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Once the driftwood was attached to the basket using cable ties (making sure the cable ties were tight enough to prevent turtle toes getting trapped), I added another piece of bark, also found at a local beach and thoroughly washed, to hide the top of the basket, and expand the basking area (photo 7). This was not attached, to allow easy access the basket, but was wedged in firmly behind the large driftwood branch.

With the filter and basking area up and running, live plants were added (photo 8) to help the turtles feel secure, and give them a constantly-available food supply if they get hungry. These plants will also help keep the water clean, utilising excess nitrates. Water from a healthy local pond was also added to "seed" the water with microflora.

Whilst this filter should help keep the water quality high, a small internal filter has been added (without any filter medium) to break up the surface of the water, as otherwise the proteins in the water rise to the surface and form a protein layer "scum". In time, hopefully the microflora in the enclosure should be able to break down these proteins and allow me to remove the empty internal filter.

If you have any questions on this filter, or setup, feel free to contact me:
Paul Edmondson
info@insectivore.co.uk



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