You only need to take out enough water to dissolve the bicarb in, 100 ml-ish. If the bicarb won't all dissolve take a bit more water.
Try 2 level tablespoons/15 ml spoons to start. Once it has dissolved, pour it slowly into the stream of water coming out of the filter. Wait half an hour then test pH. If it's still below 7.0, repeat with another 2 tablespoons.
Try 2 level tablespoons/15 ml spoons to start. Once it has dissolved, pour it slowly into the stream of water coming out of the filter. Wait half an hour then test pH. If it's still below 7.0, repeat with another 2 tablespoons.