I'm sure MrS will be here soon, but in the meantime, I go with 2g/gallon for solo cups with roots, and 4g/gallon once the plants are established (4 or 5 nodes), and then get up to 5.5g/gallon in late veg. I start bumping them up in flower, and end up between 6 and 6.5 depending on how the plant looks.
I try not to wait for signs of deficiency because then you're chasing the problem. I prefer a bit of tip burn to seeing a Ca deficiency that has been brewing for 2 weeks before showing up on the leaves!