Mixing substrates

[JFR]

I'm overhauling an existing 55 gallon tank and planning to start over with different substrate, filter system, etc. for an aesthetic change, as well as to make it more hospitable for plants.  I have extremely hard water that is slightly alkaline.  I was given 2 8L bags of the Dennerle Scaper's soil which I am aiming to use as a base, with the recognition that it will lower the pH and soften the water.  I don't have enough of this soil (and don't particularly want to purchase more), so I'm trying to figure out what to put over it.  I don't mind using an inert material on top and supplementing with nutrients.  I'm wondering about EcoComplete, but I've read that it might actually RAISE the pH.  Can someone tell me what effect that might have on the water and the longevity of the soil if I combine these 2 competing effects?  Alternatively, would I be better off with 1) more of the plant friendly substrate, or 2) regular inert gravel or something such as black diamond blasting sand?  Thank you in advance!  I've learned so much from this forum.

[Scapexghost]

It's common practice to "cap" an active substrate w/ an inert substrate. This has the benefit of minimizing to leeching of nutrients into the water. Even a small layer of active substrate will do a lot for plant growth. I would recommend gravel over sand if your goal is maximizing plant growth.

[JFR]

But would there be a benefit to using EcoComplete as a cap?  What will that do to the water parameters if the Scaper's soil lowers the pH and softens the water while the EcoComplete does the opposite?

[Streetwise]

For those of us running organic topsoil, the substrate is lasagna.