Driftwood has turned the water the colour of weak tea — does this clear on its own, and does it matter to the plants?

If you want it gone without pulling the wood, activated carbon in the filter is the direct answer and it works fast — usually visibly clearer within a day or two.

Things to know so it does not become a permanent fixture:

It exhausts. Carbon binds until its surface is full and then it is just an expensive sponge. A month is a reasonable working life; after that it does nothing and people leave it in for a year believing it is still working.

It is not selective. It pulls out tannins and it will also pull out liquid fertiliser and anything else dissolved. In a planted tank that matters — if you dose ferts, dose after the carbon has been in a while or you are partly feeding the filter. Some people run it only for a week to clear things up and then take it out, which for your situation is what I would do.

Purigen is the alternative people reach for. It targets organics, it is more selective, and it can be regenerated rather than replaced. More expensive up front, cheaper over a couple of years, and it goes visibly brown so you can see when it is spent, which is genuinely useful.

Either way, the wood keeps leaching underneath. You are treating the symptom, which is fine, but expect to repeat it a few times before the wood settles down.

It clears on its own, it is harmless, and four days of soaking was nowhere near enough — which is the useful part, because it tells you what to expect.

What you are seeing is tannins leaching out of the wood. How long it runs depends on the type and size of the piece and how dense it is: a small piece of a light, porous wood might be done in a few weeks, a big dense piece can release visibly for months. Three weeks in is early.

Things it actually does:

• Lowers pH slightly and softens water a little. Usually small in a tank with normal water changes, and worth knowing rather than worrying about.
• Absorbs a bit of light, which is the only real effect on plants. In a low-tech ten gallon this is marginal, but if you have anything light-hungry at the substrate it is a factor.
• Nothing harmful. Fish from tannin-stained water actively prefer it.

To speed it up: water changes are the honest answer, and they work in proportion to how much you change. Boiling the wood before it goes in pulls a lot out quickly and also helps it sink — soaking cold barely touches it, which is why your four days did so little. Repeated boils with fresh water each time is the fast route, but that means taking it out, which you said you would rather not do.