It depends on what you want.
As long you have the money in the chain is secure from any tax but if you withdraw your profit in fiat you are eligible for taxes.
You should convert in fiat only what you really need if you have a business running in bitcoin and you want to save tax.
If you want to pay as much tax as possible than convert it all in fiat.
Please dont be offended, but this simply isnt true. The tax authorities will not care whether you change from BTC to fiat or not, and depending on the context it can be more or less easy for them to figure out that you are doing something and not telling them about it. They actually dont even need to figure out what that is or how much you are making from it, they can just decide on an arbitrary amount and prosecute you for not having paid that.
If you want make money from selling bitcoin goods and services and not pay taxes, you still ought to report some income that is feasible compared to your living expenses in order to keep the tax authorities happy. You also need to set up some way of actually spending and withdrawing the money you make, like e.g. a no-name card.
