Thank you I will keep that in mind!Rocky, if you just want the benefits of tannins in your water, another option is to add some rooibos tea to your tank.
I don't like leaves in my Sumatra tank--they take up too much room and look out of place in a rice paddy--but my fish are mostly from black water habitats. Just get some cheap rooibos tea from amazon or the grocery store. Make sure it's pure rooibos, without any other herbs in it. A lot of rooibos teas are blends, mostly because the stuff tastes terrible! About one tea bag per ten gallons of tank will do it. Leave the tea bags in over night. Does the trick!
I like tannins but I honestly wouldn't JUST add the tannins themselves... I would want the leaves. I want to see how the gudgeons interact with it and use it in their environment. I really like the look of leaves at the bottom of tanks when I see pictures of it.