Boiling worked the best for me when I was trying to remove tannins from wood. Soaking in cold water did not. The cold water I had my wood soaking in turned a yellowish brown color from the tannins. The water I boiled the wood in turned a dark, rich reddish brown color. With that said, boiling may not completely eliminate your problem but it may help it considerably.
I do not have any experience with German Rams so I cannot advise about such a drastic water change. However, you might consider a daily series of 30% changes for a while instead. I do have shrimp and, regardless of filtration beforehand, I treat with prime and test for TDS and pH with every adjustment. .02
Easing my toes in the water