It works quite well for removing tannins but heavy tannins can stain Purgen and often times it won't turn white when recharged. Depending on the level of tannins you can use carbon to remove them. Just replace the carbon when you see the water begin to color up again. Many will argue carbon is bad in planted tanks and will remove fertilizers that the plants need but I've been using carbon in planted tanks since the 80's and have never had any ill effects on my plants. It's just a matter of choice on what you want to use.