I was going to say 'charcoal and water changes', but I deleted part of it.
Why are you trying to get rid of the tanins? It does have its beneficial effects. Is it because you don't like the look? What species of SA are in the tank and how are they thriving?
Brown water is a bother to folks who keep plants or for those who have worked hard to have 'clear' water. But as one who keeps fish that mostly thrive in 'black water', it is a welcomed sight. I had a pair of
Crenicichla acutirostrus and several species of
Apistogramma that thrived when the tank was dark brown and warm. Of course, I strived to match their husbandry conditions to their type locality.
Driftwood, as you already know, will also affect the alkalinity parameters. Keep an eye on you pH, too.