A power cut in the breeding room: what gel buys you in hours

At 2:40 in the morning the power went out on a street in Sheffield and stayed out for nine hours. The room held forty tubs of Phyllobates, three clutches on damp film, and no backup ventilation. By the time the owner got up at seven, the room had dropped from 24 C to 17 C and the humidity in the top row of tubs had fallen from 88 to 61 percent.

That is roughly what a well-built gel floor buys you: a slow slide instead of a cliff. It is not a week. It is not even two days. Knowing the real number matters, because the keepers who assume a gel floor is a battery tend to be the ones who lose a clutch.

What a gel reservoir actually holds

Take a standard 30 by 20 cm tub with 5 cm of substrate at 4 percent gel. The dry substrate weighs about 600 g, so the gel content is around 24 g of powder. Fully hydrated at 300 times its weight, that is 7.2 litres of water bound in the floor. That number sounds enormous and it is also useless, because most of that water is held too tightly to evaporate at any meaningful rate.

The usable figure is what the floor can give up into the air above it without collapsing. In practice, a tub of that size with the lid on loses 8 to 15 g of water a day at 22 C. The gel is not the limiting factor at that rate. The limiting factor is the surface area of substrate exposed to air and the ventilation rate of the lid.

The three-hour test you can run tonight

Weigh one full tub, lid and all, on a kitchen scale. Write the number on a strip of tape on the side. Put it back, run your normal routine, and weigh it again 24 hours later. The difference is your tub’s daily water loss in grams. Do it three days running and average.

Now you know your buffer. A tub losing 10 g a day drops roughly 4 to 6 percent relative humidity per day once the free surface water is gone, so a floor that starts at 90 percent takes about a day and a half to reach 70. That is your honest window in a power cut: 24 to 36 hours before you need to intervene, not five days.

Where the buffer runs out first

Small tubs lose humidity faster than large ones because surface area scales with the square of length while volume scales with the cube. A 15 cm juvenile cup can drop 15 points in twelve hours without power. A 60 cm tank in the same room might drop 8. If you have a mixed room, protect the small containers first and let the big ones ride.

Ventilated lids are the other variable. A tub with six rows of drilled holes exchanges air far faster than a tub with two. In a normal room that is fine, because your misting replaces the loss. In a cut, it is the difference between a 24-hour buffer and a nine-hour one. Keep a roll of cling film or a few solid lids in the room for exactly this situation.

A power-cut plan that fits on one card

• Close down ventilation on the smallest tubs first, then work upward
• Do not open lids to check. Every opening dumps the humid layer you are trying to keep
• Move tubs off the floor and away from external walls, which cool fastest
• Wrap the rack in a breathable blanket rather than sealing it in plastic
• Keep one battery hygrometer in the room so you can see the slide without guessing

The failure I see most often is not the cut itself. It is the panic misting at hour two, which soaks the floor, drops the temperature further through evaporation, and leaves the animals sitting in cold wet substrate for the rest of the outage. A gel floor is designed to release water slowly. Let it do that.

If you are setting up a room from scratch and want the numbers behind the substrate spec, the SAP powder product range lists swell capacities by grade, and the difference between grades matters more in a small tub than a large one.

Run the weigh test on your three smallest tubs this week. Two of them will tell you something you did not know about your own room, and the fix is usually a lid, not a bigger gel dose.