I never look this far down on the forum, but, I have interesting info to share. I've been keeping a tank with tetras in it for years and years now. I was at the petstore just the other day, and found a bottle of stuff from TetraAqua called, "Blackwater Extract." I talked to some people, looked online, etc., and then bought it and used it just today. From the bottle...
"Blackwater Extract contains trace elements, vitamins, and valuable extract of peat. It creates an environment similar to parts of the Amazon River and other natural, blackwater biotopes. Blackwater Extract promotes fish activity levels. When added to the aquarium, a light yellow color will appear. blackwater Extract is an excellent conditioner for all soft water fishes included: discus, angelfish, tetras, and killifish."
Ingredients: Vitamins B2, B6, B12, Nicotinic Amide, Panthenol, Biotin, and Peat Extract.
Supposedly this will soften the water a bit, and will imitate natural blackwater conditions without all the dirty hassle.
Seeing as I only added it today, I can't attest to any long term effects, BUT! I will say it did make the water become tinted light yellow/brown. I have not seen any immediate adverse effects to the fish, and really like the color the water has taken on. Hope you get this before you start making huge expensive decisions. This might save you some time/money/trouble!