I think that the PPM and hardness in my area just messes up everything. I think the water gets crowded and not allowing the cal/mag to do it's thing. Recently in an attempt to save my grow I switched to bottled RO water. It's a pain to lug it around, but the plants are looking better and yellowing less.
Next grow I want to get things right. I will only use RO water and supplement with Cal/Mag. Now I need to decide on grow medium and nutes.
What is the ppm of your tap water? You're right, if it's high it reduces the ppm's available for nutrients. But, going to pure RO water with calmag may not be the best solution. Calmag acidifies the water which may lead you to use ph-up which adds K, more ppms. It turns into a vicious cycle.
I would suggest mixing RO and tap to get 150-200 ppm water. You won't have to use calmag to replace minerals in 10ppm RO water. You won't have acidic water from the calmag. You won't use phup (assuming your nutes in combination with higher-ph water results in a decent 6.2-6.8 range.
You're asking all the right questions. I'm sure you'll find what works best for you. At one point you mentioned a desire to keep it simple. I use Pro-Mix HP, Kellogg Patio Plus and perlite. I mix them 50-60%, 20-25%, 20-25% and add 2 Tbsp fine-textured dolomite per gallon of medium. It's not very expensive. It's a good, well-draining soil. (I aerate the soil by pushing a 1/4" rod into the soil occasionally.). Nice texture. Not heavy, not woody, not fluffy like 100% peat.
It's nothing special. Some light nutrients from the Kellogg product. You can mix it in an apartment inside a plastic bag. 2-1-1 scoops of each product, and shake the bag for 30 seconds. Holds the dust inside. You could use a Home Depot bucket with a spin-on lid. Shake it or roll it back and forth on the floor.
