Yes, Ca, Mg and potassium bicarbonate are for reconstituting RO waters minerals/KH. You can also add a touch of sodium bicarbonate if you want to raise PH/KH a touch more.
You need to find fert dosage amount of those in relation to your planting density and type of plants, lighting and co2 systems. Doesnít sound like you have co2 system and you havenít mentioned what light and plants you have. A pic of tank would help immensely, itís very, very hard to recommend dosing if you donít know what your dosing for. To much ferts and light youíll have a algae farm, to little and plants wonít have enough food, growth will stall and algae will again have upper hand because plants canít outcompete the algae when their starving. Itís all about finding balance between light, carbon availability, fert dosing plus maintenance and water change routines.
Go to rotalabutterfly site, figure those amounts for you tank and do both EI low light weekly and full EI dosing and read those instructions. Your dosing rate will be somewhere in between those amounts. I myself would rather mix ferts up in a liquid solutions do dose with that. Itís a 2 bottle system, one for macro (NPK) and other bottle for micros.
NilocG dosing page has some premix solution formulas for EI dosing as well as for doing PPS Pro dosing. Do the 5ml per 20gal solution, 2 500ml bottles, one for NPK, one for micro mix.
Now remember that will give you a 5ml per 20gal EI dosing solution for tanks that have good light, co2 injection and fast growing stem plants, youíll dose that 5ml amounts 2-4x a week.
Now if your tank is med light, no co2 injection and a bunch of easy low demand type plants you can cut that amount to 1/3 or maybe 1/2 and only dose 2-3x a week.
Itís about finding that balance, making sure that plants always have the 12+ nutrients they need to fluorish in solution but also not dosing in gross excess. Donít go reading what someone on here doses for their mega lighted, co2 super charged system and try applying it to your tank unless it fits those parameters.