It doesn't sound like you have fish that would be sensitive to the lower pH levels, but if you really want the color out, there IS one way I know of to do it, and it won't hurt anything, but it will cost you a few $'s.
Here's a link telling about it, it's called Polyfilter: http://www.poly-bio-marine.com/polyprod.htm
You can order it from Dr's Foster & Smith online at: http://www.drsfostersmith.com/produc...pc=1&N=0&Nty=1
I know it works... and I will only disagree with one point made in the info page about it... it does not replace carbon. If used long term, Polyfilter will further drop your pH level, so this is a temp fix, which is what you need. I have done a lot of product testing over the years, and Polyfilter was one of my favorites for a "quick fix" such as yours. If you do daily water changes, that will help to keep your pH stable, if not bring it back up just a bit... but do SMALL changes, no more than 5% - 10% each day, so as not to shock the fish.
I have used Polyfilter in the past for removing tannin staining in my water, and it works pretty fast. Even though it will change color right away, don't change it for 48 hrs... do this for about a week, then leave it out for a week... if you need more removed, repeat for another week. It may not remove ALL of the staining in that amount of time, but it will take out most of it. Remember to put it into the filter, so water flows THROUGH it at all times, and remember to use as big of a piece as will fit into your filter. If you have more than one filter, you can run it in both. This will not bother your biological cycle in any way, so everything else you do can remain as normal.
Carbon would also take it out, but you would use a lot more carbon than Polyfilter to do it, and it would in general be a pain in the butt! (not to mention more expensive and taking longer)
I hope this helps!
Happy New Year!