Fwiw, wood may continue to leach for, possibly, years. I have wood that is still leaching, after 19 months and extensive soaking first. It does depend on a few factors; species of the wood, age, how long it was soaked before use. Boiling can help move a lot more tannins out faster, but there is a limit to how long you can cook the wood. Heat causes some softening of the fibres, so extreme cooking might shorten the life of piece in the tank, possibly. I doubt many of us have the patience or time to overcook wood though
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I now use bleach when I soak wood, as it seems to help remove more tannins faster, but it will also, I must warn you, lighten the wood. Only the surface layers, and it can be sanded off if you don't care for it, but that's more work too. It will always be much darker looking in water than it might look when dry. Bleached wood can look quite white when dried out, but it looks fine to me in the tank. It shows nerite eggs less obviously, which is nice, since I have a number of them.
I have wood that I soaked for upward of three months in a bucket with regular water changes, that still leaches in my tanks a year later. Mopani wood, a common one to find in stores, which is both light and dark in colour, appears to leach a LOT. Dark brown wood, very heavy, often called Malaysian driftwood, also still leaching over a year later, just less as time goes on.
With time the colour of the leachate weakens, so you stop getting tea water and it's more yellow. It lightens with each water change, and continues to get weaker as time goes by. I have yet to find out when it stops, but I'm at 19 months with the first pieces I used now. Since there are younger pieces in with them, it's impossible to say which ones are contributing the most colour but I find I don't mind the yellowish tint. It's clear and clean, that's what I care about most.
