The main problem of a properly installed tank is sediment. Depending on the amount of silt in your water, it may need to be cleaned out occasionally.
In some tinacos, fungus growth can be a big problem although Tinacom tinacos claim fungus resistance and mine hasn''t incurred any problems in that regard yet. The tinaco at another place I lived had a horrible fungus problem but it was hardly ever used and evidently not of a fungus resistant material.