The high CEC is why I am going with something close to EI dosing even while I am cycling the tank. Get lots of ferts in there to load up the substrate.
I have run a lot of tanks with Soil Master Select, and have no problems with the low to zero KH and low pH. Once the system is cycled the bacteria can slow down and it is not a problem. It is just while trying to build up the population as quickly as possible that I want to maintain harder water, higher pH. Then it can crash, and that is fine with me. It will match most of my other tanks.
Then I can move the fish over. I will be putting my Filimentosa Barbs in the 88. They are somewhat plant-nippy, so I am researching plants that are OK with Goldfish under the assumption that they will be OK with the Barbs, too.
My long posts reporting what is going on can be summarized really quickly:
This substrate removes the KH, thus allowing the pH to drop.
This substrate has high CEC, so loading it with fertilizer is a good way to assure the plants have a good reserve.
What you do with these facts is up to you.