Tannins are actually good for many fish. It us humans who don't care for how it looks, because yes, peat and wood can both turn water yellow or brown. New wood, if not soaked or boiled well first, can turn water dark as coffee at first. It gradually lightens with time.
I soak wood for months in a bucket first and often use bleach to speed it up and lighten the wood as well. Rinse thoroughly and use extra dechlor' if I bleached it. Boiling is too much effort for me.. and the stove is quite small, making it hard to do for large pieces anyway.
The question really is, do you truly need to lower your pH at all ? Unless the fish you intend to keep need acidic pH, I doubt you need to do anything to the water other than dechlorinate it. Fish are quite adaptable, most common species would vastly prefer stable tap pH over changing pH. Over the past year, I've noticed the pH in my tanks is now around 7.2, when the tap water itself is around 7.6. Old tank ? I am not sure, but it is lower than the tap water now, and did not used to be. I do regular water changes, so they do get added new water.
Adding wood does very slightly acidify, but the effect is no more permanent than the leaching is. Peat is the same, must be renewed to maintain the effect. It is a lot of work for very little or possibly no gain to you or the fish. Trying to get an exact pH, in any water, is quite hard to do. And constant adjustment is very stressful for fish. Unless your tap water has issues that make it totally unsuited for fish, say, chemicals or other contaminants, usually it is best to use tap.
Or else go for RO and remineralize it to the required hardness and pH, which means buying the RO water, or an RO filter system, plus the mineralizing products. Costs money. RO filters also waste a certain percentage of every gallon they filter, which can't be recovered, and you pay for that water.
So give it some thought. Being obsessive over a few points in pH is liable to make you crazy and your fish will not thank you for it either.