Let me see if I can help some here...
Post 8 in that other thread is referring to C
EC in terms of substrates (C
UC is a very different thing, and yes much more specific to SW aquariums). CEC is Cation Exchange Capacity, which is a calculated value that is an estimate of the soil's ability to attract, retain, and exchange cation elements (
Source). CEC is important in planted tanks when using these types of clay substrates as a higher CEC means the substrate is more prone to absorbing nutrients (the ferts you dose into the water column), and then being able to supply those nutrients to plants via their root systems.
SMS is an old substrate that is no longer being manufactured (it's what I have in my 125g tank). It stands for Soilmaster Select, and it was replaced commercially by what is now called Turface a few years ago.
Power Sand is an element to the ADA Aquasoil "system" of substrates that you're supposed to mix with their Aquasoil substrate. From the ADGshop website, "Power Sand is composed of porous volcanic stones to secure proper water circulation and of organic materials including fertile peat to provide rich nutrients to aquatic plant roots. Ideal conditions for bacterial activity and development of plant roots are created and maintained for long periods with Power Sand."
EI, as stated above, is the Estimative Index method of dosing fertilizers. The EI method summary is that you dose enough ferts in your aquarium to make absolute sure that enough nutrients will always be available to your plants, then at the end of every week you do a very large water change to get rid of the excess before you start again the following week.
PPS Pro is a different strategy that aims to provide, on a daily basis, the amount of ferts that your plants will need for that day. The concept here is to not allow the nutrient levels to get too high, which causes algae issues. PPS is a little more difficult to deal with, especially in the beginning, because running out of a single nutrient (and not the others) is a bad algae scenario to be in as well. It takes time to get things balanced out, but it is my preferred method of use once it's dialed in. There's also a lot more leniency if you just can't do a PWC one weekend since you don't have a huge excess of nutrients in the tank that must be removed before it's too late.
Zeroing in the right balance of all those things you listed just takes time, especially ferts. We in the community give guidelines of where to start out (i.e. how much ferts to dose) but in all it is really up to you to pay attention to your tank (no 2 are completely alike) and make tweaks along the way.
CO2 is pretty straight forward. 30-35ppm of CO2 is a nice, balanced place to be. It provides plenty of CO2 for your plants, while not saturating the water so much with gas that there's no O2 for your fish.
As for substrate selections, that's a whole lot of personal preference. Different substrates provide different things, like you probably read about in the AS vs AP thread.
I hope that cleared some things up for you. If not, ask away and I'll try again. =)
It sounds really really hard and complicated, I know it does. All you really need to fully understand is that you're going to need patience, you're going to deal with algae issues, and that AA is here to help you through it. There is a very steep learning curve to planted tanks, but the benefits in the end are awesome!
Also, depending on the types of plants you want to do (you only said low-light, low-tech) you may not need to worry about any of this. Many of the easy, beginner plants will do just fine without anything special at all. Standard aquarium gravel, regular lighting and nothing else can grow some plants just fine, your selection of plant types is just limited to those few easy plants if that's what you're looking to do.
