Mopani wood killed fish?

I boiled mopani wood for hours until water looked clear and then let it cool. I then put it in the tank. All my levels were fine before the wood. The tank has goldfish kuhli loaches and bristlenose pleco. I got up this morning and one of my goldfish is dead, two kuhlis are dead and the rest of the kuhlis look like they are about to die. What happened? Did the wood do this? It did leach some tannins in the water but I researched before I put the wood in and everyone said the wood and tannins wouldn't hurt anyone. It looks like I am going to lose everyone. What happened? What should I do? Are kuhlis allergic to tanins or something? I removed the wood and most of the colored water but don't know what to do now.