when to start kalkwasswer dosing......

[Aquattro]

Marco, you're paying extra for the Reef Crystals and you don't really need to. Instant Ocean is the defacto standard in salt mixes. If you prefer the Reef Crystals, my understanding is that Kent is the same salt. The advantage to RC/Kent is that the Ca is a bit higher than IO. If you're dosing kalk, this may help you maintain levels. Kent is generally a bit cheaper than IO.
On the kalk dosing issue, you certainly won't need to dose a saturated solution until you have corals that consume it. The best thing to do is calculate your total alk consumption and dose accordingly. Also, until your tank has fully cycled, any acids (eg. NO3) wil eat up your alkalinity faster than you can dose it. I wouldn't dose until you have zero nitrates. Using a DSB, this could be up to 2 or 3 months.
Finally, you may want to consider adding vinegar to your kalk as this tends to give you a more complete reaction within your solution and reduces precipitation of carbonates. I can give you additional info on this if you decide to look into it.