My latest tea experiments have all been about the water used to brew tea. Some things I've discovered aren't exactly new, but they are things I never thought about before.
I started experimenting with my water after learning that I have to treat water so that I could brew different beers. Tea and hops seem to act the same, so I'm basically replacing "hops" with "tea" when reading the homebrew books. Calcium sulfate (gypsum) emphasizes a cleaner 'tea' flavor. Calcium chloride emphasizes bitterness. What really got me started was learning about bicarbonates. I still don't understand it completely, but it sounds like they combine with calcium to form scale. They raise the ph of the water, and contribute a harsh bitterness in 'tea'. To get rid of it, the water needs to be boiled so it will precipitate out as calcium carbonate. If you heat water for green tea by stopping it at the right temperature, the bicarbonates might not come out. So maybe boiling to "open up the water" is just getting rid of any bicarbonates that might be in the water.
So, I started boiling water for every tea, and went back to tossing water back and forth in pitchers to cool it for green tea. The next experiment was water hardness. We all know that dark teas like hard water, and greener teas like soft water. I finally have the ability to find out my water hardness and to change it. Using aquarium test strips to find the hardness, the brita water I've been using has a general hardness of 30ppm and almost no carbonate hardness. 30ppm is very soft, so I started adding gypsum to brita water to raise it to 70-150ppm. It made a huge difference in the brewed tea. It came out more flavorful and mellow.
Sometime later, I decided I wanted to avoid the expensive brita filter, and just dechlorinate using activated carbon. As long as the chlorine is removed, the tap water here is actually pretty good. I ran out of bamboo charcoal a long time ago, but I have some high quality aquarium charcoal (pro-carb) that I got around the time I posted the bamboo charcoal experiment. I got a few 1 gallon jugs, and let tap water sit in it a few days with the carbon. It takes about two days, but it does remove any chlorine smell. After a while, I noticed something weird. Green tea started coming out unusually dark. Since water hardness is usually the cause of that, I stopped adding gypsum. Although, that didn't solve the problem. Green tea still came out unusually dark.
So, here's my results of water with aquarium charcoal vs. bamboo charcoal. Aquarium charcoal removed chlorine in about two days (bamboo charcoal removed about the same). Bamboo charcoal seemed to sweeten the water a bit, so it's likely that it added some hardness. When I finally tested the water with aquarium charcoal, it hardened it significantly. Tap water originally has 60ppm general hardness (40ppm carbonate), but with the addition of charcoal alone, it raised to 180ppm! Dark teas could handle that, but green tea can't. So, unless you only brew dark teas, I don't think aquarium charcoal is the way to go.
I ordered some bamboo charcoal last week, and I'll test it once I get it to see how much hardness it adds in comparison.