Also note that Equilibrium does not dissolve instantly, at least not completely. There will always be undissolved "crumbs" left in the bottom of whatever you mix it in which should be added to the tank. Better to pre-mix before adding to tank so you can stir / shake to help mixing. I find the GH readings increase by about 1 degree when comparing measurements made immediately after mixing to those the next day, so be aware of this so you don't add too much!
16g will increase 80 litres of water by 3 dGH (as per instructions on tub)
So 1/15th gram will increase the hardness of 1 litre by 1 dGH
Therefore work out your volume of water (in litres) and multiply this by 1/15 (or 0.06667) to calculate how many grams you need to add to increase hardness by 1 degree.
To begin with, raise the water in the tank to your desired hardness, but do it slowly (over days / weeks). So calculate how much to add based on tank volume.
Once your tank is at desired hardness, just add Equilibrium to the water change water (based on water volume to be added, not whole tank) to match hardness to that in tank. Keep an eye on hardness in tank as it may drift over time and adjust by under or over dosing w/c water to correct.
Top up evaporated water with soft water (i.e. no Equilibrium added) as minerals don't evaporate, so no need to re-add them. Ideally top up with RO / distilled water as your tap water will still be adding addition minerals, but you can correct for this by adding less Equilibrium at next w/c.
Hope this helps, James