Generally speaking, there are no income tax or CGT implications if you're not in business or carrying on an enterprise and you simply pay for goods or services in bitcoin. However, if bitcoin is used for personal use and you have a capital gain or loss of $10,000 or more from the disposal of the bitcoin, capital gains tax will apply.
Capital gains and losses need to be reported in your income tax return and you would pay tax on your capital gains. When capital gains are made, they are added to your assessable income and may drastically increase the tax you need to pay. This income or loss is part of income tax, not a separate tax. Discount of 50% on capital gain tax is available if cryptocurrency was held more than one year.
For further information on the treatment of tax in relation cryptocurrency please contact DD's Taxation and Accounting Centre.