I have never used blackwater extract, I think that it is mainly tannin, if so I have known a couple of people who used water that they boiled black walnut husks in and then added a little to get that blackwater look but to me it just seems like one more thin to goof up, the right lighting, planting and background will give you the same effect. I read your thread starter post and see that you already have the 55g tank. While bigger is always better I think that a 55g is a nice tank and as you get into the hobby you will find that as you upgrade the older tanks turn into useful secondary tanks like for hospital tanks, feeder keepers, quarantine tanks, or specimen tanks for fish that don't play well with others. I kept a marbled goby in a 55, and an american eel in another.