Pacman frog burrow humidity: substrate depth versus gel share

Six inches of packed coir with a 2 percent gel share read 78 percent at the bottom of the burrow. Four inches with a 5 percent share read 71. Same frog, same room, same week, two tubs side by side on the same shelf. The keeper had bought more gel to fix a problem that a deeper floor would have solved for nothing.

A Pacman frog does not sit on substrate. It disappears into it, and what it actually experiences is the air inside the pocket it digs. That pocket is shaped by how much material sits above the animal and how well that material holds onto its water. Gel moves the second number. Depth moves both.

Depth is the buffer, gel is the reservoir

Think of the floor as a stack of lids. Every extra inch of firmly packed coir slows the exchange between room air and burrow. In a heated room at 24 C and 35 percent ambient, a four-inch floor dries downward at roughly a centimetre a week. At six inches, the dry front takes close to twice as long to reach the frog, not because the material is different but because there is more of it to cross.

Gel works differently. Hydrated polymer holds water in a form the surrounding fibre can draw back on, so a mix containing gel loses moisture more slowly at any depth. But it cannot manufacture distance. A two-inch floor with a heavy gel load still leaves the frog digging in the top layer, right where the room air pulls hardest, and that is the layer that fails first when a heat wave hits.

Where the gel share actually earns its money

The share matters most in the middle of the depth range. Below about 4 percent by dry weight, a coir mix stops holding a burrow wall and slumps after two or three days of digging. Above 8 percent, you are paying for water the frog will never reach, and the floor turns springy enough that a determined adult can push through it into the drainage layer.

Animal size shifts the number as well. A 50 gram juvenile digs a shallow scrape and benefits from a higher share near the surface, where the drying happens. A 400 gram adult excavating a full-body chamber wants structure more than stored water, and structure comes from depth plus long fibre. If you are rebuilding after a dry winter, this is also the moment to check the room rather than the sack.

• Juveniles, 7 to 10 cm of floor: 5 to 6 percent gel by dry weight
• Adults, 12 to 15 cm: 3 to 4 percent
• Large females, 15 cm plus: 2 to 3 percent, packed firm in three layers

A starting mix and how to move it

Mix dry powder into dry coir first, then add water in two goes and turn the whole batch twice. If you hydrate the gel separately and fold it in, you get pockets of pure gel and pockets of bare fibre, and the frog finds the wet pockets and sits in them until the skin under its vent stays damp for days. That is how bacterial skin problems start.

The guide on humidity control for exotic pets covers the room side of this in more detail, including what happens when ambient drops below 30 percent for a week.

The tub that failed at four inches

A customer sent photos of a juvenile albino with pink, irritated skin across the underside of both thighs. The floor was four inches, the gel share was 6 percent, and the hygrometer on the back wall said 82 percent. The hygrometer was right and irrelevant. It sat 20 cm above the substrate, in the humid layer that never touches the frog. Down at burrow level the reading was 64.

We rebuilt that tub at 12 cm with a 3.5 percent share and the skin cleared in eleven days without any medication. The lesson is not that gel is bad. It is that a hygrometer measures the air where you hung it, and a burrowing frog lives somewhere else. Probe the burrow, or push a cheap sensor down a corner and leave it there for a day.

Before you buy another sack, dig a test hole in your current floor with two fingers and feel the bottom. If it is cool and damp, the depth is doing its job. If it is dry and loose, no gel share will save it. Work out the depth first, then the share, then the room.