DIY instructions are readily available but I can give a quick Coles notes here (apologies for hijacking the thread). You can use this stuff straight, but personally I prefer to balance my buffer before I add it (it will do this on it's own in the tank but will cause a pH shift while doing so). I do this by baking some of the baking soda in the oven at 400f for about an hour (this converts the bicarbonate to carbonate). Then I add 1 part of the baked stuff to water and mix until dissolved, then 7 parts of the non-baked stuff and mix until it is mostly dissolved. If you add in the opposite order it will be fine but harder to dissolve. You will get a saturated solution using about 100g total (~15g baked+85g nonbaked) for every litre of water (there will actually be a bit of powder leftover on the bottom that will not dissolve so shake before each time you add to your tank). I use RODI water but you can get distilled water from a pharmacy, or tap water should be fine too. A 500g box makes up about 5l, with a total cost of a couple of bucks (as compared to $100+ in the stores). This is not a 'close match' to store bought stuff, it is EXACTLY what the stores are selling you, the exception being the pH 'up' versions that have borates added, and some companies vary the ratios around the 7:1, but this matters little as your the naturally occurring chemical reactions in your tank establish an equilibrium between carbonates, bicarbonates and CO2, so varying the ratios you add will have no long term effect (thus you could add straight baking soda, but the short term pH shift will be a bit more stressful for your critters). Short term effect is a shift in pH of a few of tenths for a few hours. This is the only buffer I have used for several years, I'll let you be the judge on whether or not it works...
