Coco can be used both dry and wet, which means you don’t have to use two different substrates (moisture-retention substrate for wet hideouts and a drier one for the rest) – you just keep the hiding place moist and the rest of the terrarium dry.
However, there are a couple of issues with coconut coir.
Bark/coco-fibre/peat etc are not ideal for leopard geckos due to there moisture. Too much moisture not only causes mold growth but also upper respiratory problems especially in leopard geckos.
However these could be dried out to reduce the humidity problem but they still carry the risk of impaction.
In the case when coconut coir is kept dry, it produces fine dust, which can, in theory, harm your gecko’s respiratory system. Secondly, like other loose substrates, coconut coir can be swallowed in quantities that can result in impaction – though most geckos don’t seem to perceive coconut coir as a “nutritional supplement”, so they won’t try to eat it on its own.
However, many consider that these properties do not make coconut coir worth the risk of using it in a gecko tank.
If you’re still opting for coconut coir, make sure that you get a brand that is made out of organically-grown coconut and, ideally, intended for use in reptile and amphibian tanks.
Substrates that cause major problems:
• Sand for Gecko under 6 months. Causes suffocation.
• Bark. They are easy to swallow and are known to cause suffocation.
• Cedarwood and pine because of its toxicity.
• The soil used to make pottery because Gekon can eat some of its unhealthy ingredients.
• Crushed walnut shells
• Wood Chippings
• Sharp substrates
• Corn cob