Candling Leopard Gecko Eggs: How & Why
How it's done
In a dark room, hold a small, focused light source (a phone flashlight works) gently against the shell to shine light through it, without rotating or flipping the egg from its original position — leopard gecko eggs should never be rotated once laid, since this can dislodge the embryo.
What a viable egg looks like
A developing egg typically shows a network of fine blood vessels within the first couple of weeks, progressing to a visible darker mass as the embryo grows — the egg also generally firms up and stays a healthy white to slightly translucent colour.
What a bad egg looks like
An infertile or non-developing egg tends to stay uniformly translucent or yellowish with no visible veining, and may develop mould or a collapsed, discoloured shell over time.
How often to candle
Candling too frequently isn't necessary and adds handling stress to the incubation process — an initial check a week or two in, followed by occasional spot checks, is generally sufficient.
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A single adult leopard gecko needs a 20-gallon long tank as an absolute minimum, with a 36x18 in (40-gallon breeder) footprint now considered the recommended standard — plus a secure lid, an under-tank heater on a thermostat, a thermal gradient, at least three hides, and a shallow water dish.
Set up in this order: substrate, then heat source wired through a thermostat, then hides and water dish, then decor — and run the whole enclosure for at least 24–48 hours to confirm stable temperatures before your gecko moves in.
Hatchlings can start in a 10-gallon tank or tub, juveniles do well in 20 gallons, and adults need a 20-gallon long as an absolute minimum — with 36x18 in (40-gallon breeder) now the widely recommended standard, not just an upgrade.
Heat a leopard gecko enclosure with an under-tank heater and/or overhead heat source (halogen or deep heat projector) wired through a thermostat — a thermostat is mandatory, not optional, and heat rocks should never be used.
Leopard geckos can survive without UVB using dietary D3 supplementation, but current husbandry guidance now recommends low-level UVB (roughly 2–6% T5) as best practice — it improves D3 synthesis, bone density, and natural behavior, and views on it have shifted significantly from older nocturnal-species advice.
Keep ambient humidity around 30–40% across most of the enclosure, with a dedicated humid hide raised to roughly 70–80% to support smooth, complete sheds.