If the sand is to fine it compact's like standing on the beach at the edge of the water, know how your feet kind of sink, it choke's the plant and that will cause the root's to rot, so a bit more course is good, the root's need/want free room to move=better growth.
So if you have used it in the past without any trouble, then maybe it is not to fine, but course is better, but you don't want sharp jagged sand either, tough on root's when planting and uprooting.
A lite dusting of peat would be benificial even with that soft water, (I like soft water)
I would add just a smidge anyway.
To make the pH a bit more stable, you would just need to add a bit of baking soda to increase the KH which is the buffer for the pH... simple, or Seachem EQ will increase both KH/GH. or. ha,, learn how to use surface aggitation to airate the water which in turn increases pH by adding 02 and off gasing C02, this way you dont need the buffer compound's added at all.
Overall the plant's really benefit from the decomposing organic's the peat has to offer.
Hope that help's clarify thing's a bit.