I have a 3ft long planted tank which my plants are growing like crazy in.
My PH in this tank is below 6, can't even test how low because I don't have a meter, just the test kit which doesn't go below 6.
I keep and breed my Taiwans in this tank. Here is how I set it up.
I put a layer of Shult'z Aquasoil on the bottom (this is a clay based soil, I think you can get it in CA as Turface?) on top of this I used a layer of Shultz Peat Moss (its the finer stuff, not chunks like Laguna Peat Moss)...wetted down with a little water to make sure it didn't float. On top I put an additional layer of the Aquasoil enough that the peat moss will not come/show thru. Fill the tank up slowly by pouring water thru the sponge filter so as not to disturb the soil setup.
I becomes a sandwich
but it has a great effect on the PH levels and produces great plants. I use RO/Mixed water in this tank and have CO2 on it too, but even in another tank without RO and CO2 the PH is 6 or below.