There is considerable confusion about substrates. Some stems from advice given at pet shops...other from outdated books. Following is brief description of the more commonly recommended substrates and any associated problems
Rabbit Pellets (alfalfa pellets):
This are often used because they are edible. However its too high in protein to be eaten on a regular basis. It is also very dehydrating so frequent soaks are needed. Young torts would need soaking daily. It is also hard to walk on and can lead to deformities in hatchlings. It also molds very quickly and can cause eye and respiratory problems.
While easy to clean and cheap, it doesn't provide micro climates. Its very dry so frequent soakings are needed. It also poses a fire risk from basking lights and heat emitters.
There are a number of recycled paper products (ie. carefresh) that are used as substrates. These have similar problems as rabbit pellets and newspaper. Also some torts like to eat it which leads to impactions if they aren't soaked frequently.
Pine shavings and cedar chips:
These can emit toxic fumes especially when heated. They are also far too dry.
Hemp /aspen shavings:
In Europe hemp is a popular substrate . Those that use it highly recommend it, but its unavailable in the US. Some people are using aspen instead and it seems to work well. Both may work for some species, however they are not suitable for Russian tortoises.
Cypress mulch and hardwood mulch:
These are ok in a pinch, but work better for larger species.
This product is sold with the idea that if its ingested it will provide extra calcium. Its very prone to clumping. It has been implicated with impaction and causes eye irritation. If mixed with loam or coconut coir (Bed-A-Beast) it can work .. but its far too expensive.
These are coconut fiber (coir) and are similar to peat moss. They come in compressed bricks. The bricks are expanded by soaking in hot water. Some site express concern for gut impaction due to the fiber expanding in the intestines. However if properly "expanded" it poses no threat. It does not shrink when it dries. For most tortoise species its too moist (or too dry) to be used by itself. However mixed with play sand its the perfect substrate.
This has the same problem as calci-sand when used by itself. But when mixed with coir and kept moist, its ideal.
Play Sand/loam (coir) mix:
This is by far the best substrate. The amount of moisture can be easily regulated. Also it easy to create a higher moisture/humidity (substrate moisture is more important than humidity) area as well as a dry area in the same pen. This way the tortoise has a choice of micro-climates. Loam is the best choice and is readily available in northern states and the UK. However here in the south its scarce. So I use coconut coir instead. This has work well over the past 15 years for a number of species I keep. Hatchlings also do well on it