Really depends on the type of fish. Correct me if im wrong but Plecos etc actually benefit from bogwood etc as it improves their digestive system. While it may make you colour undesirable the tanins it is leaching are not harmful to most fish species, so its not really a problem unless you find it unsightly.
It won't effect the fish, if you want rid of it just put some active carbon in your filter. (assuming you're not treating any of your fish, carbon will remove any medication).
Carbon will also remove minerals and other things in the water you want to keep. Best way to treat tannins is to let them leach out and keep doing small water changes every few days. Most fish seem to like the tan colored water anyways so it certainly doesn't hurt them. It's just not as aesthetic looking as crystal clear water.