General

it's just the concentration and irrelevant to frequency of application.

Low meq (milli-equivalents) in soil refers to a low Cation Exchange Capacity (CEC), meaning the soil has a reduced ability to hold positively charged nutrients. Most people grow with low meq. Think of it more like applying a template onto a medium, a template of minerals, because the soil doesn't have high meq it cant store many cations, 98% of minerals uptake through soil solution, 2% through soil particles, most soils are just moisture retainers for soil solution and not storage devices for soil particles. Plant roots remove cations from the soil solution, which are then replaced by cations from the soil particles. But because you cannot store many cations, you need to apply a ratio or template of nutrients on a more consistent basis called fertilizers. When to fertilize(apply template)? is based on EC level. Water, water, water till EC drops then re-apply the template onto the medium.

It totally depends of the brand you are using, the medium you choose and the amount of light they will have. If you use organic based products they need to be decomposed to inorganic forms by root and ryzoshpere/bacteria action -some of them are partially quelated to enhace absortion-, usually this products tell you to add it everytime but to really know how much you should add you need meters to measure things, imo having a TDS/EC meter is mandatory -as a ph is- to know exactly what are you doing, measuring the outlet of the pot will give you information about the roots and if they are in a saturated medium or if they are in fact lacking nutrients. Using the boards that brands give you are orientative that is really helpful, but it totally depends of many other factors to avoid overfertilization or underfertilization.