Tannins

I have a large piece of cork board backing making up the waterfall and backsplash in my paludarium, it was too big too boil, and now is constantly filling the water with tannins. I don’t mind it, but I’m worried for my shrimpies since they can affect pH. any ideas on what I should do it’s been a couple months and shows no sign of stopping. the water section is probably three gallons after all the sediment and plants and hides are added.