1.) Let the wood soak in the tank for 4-6 weeks. Yeah the water will change color but you cannot stop it, chemicals do not work - only dilute the process, trust me...lol
2.) Pull the wood out and soak it in boiling water - take the existing (colored) water from the tank and boil it, do not use clean water - I boiled the tank water from the stove and dumped it into a huge bucket then let the wood soak in the bucket. Soak each piece for an hour or 2.
3.) While the wood is soaking do a complete 100% water change on the tank, vacuum the gravel real good, clean all decor, etc. Put your fish in bowls or temp containers while you do this. Cover then slightly so they will not jump out...I have mad jumpers...lol
4.) Do not clean/touch your filters.
5.) Fill the tank with clean water (make sure it's the correct temp), apply some Seachem Prime if needed. Turn your filters back on.
6.) Put the wood back in, put the fish back in.
Tank/water should be crystal clear.
If the wood continues to leech after this, let it sit 4-6 more weeks then repeat the process.