The substrate looks fine and sounds good from what you've described. What's your reason for thinking it needs to be changed?
Well I'm slightly limited to where I can plant because the JBL Manado substrate is in tubs so I haven't got much flexibility on where I can plant. Also, it has come through from below in places when I've been planting or adding the root tabs so it looks scruffy! Hopefully the Marco Polo will settle in and spread to cover that though.
I might just keep this tank as it is for now and wait until I get somewhere bigger with room for more tanks
The dragon stone was £5 per lump which seems reasonable.
And yes, I love the minnows too. Always on the move, and they coloured up nicely, with the red on the fins coming through very strong after only a day or so. It's fascinating watching the males showing off, racing each other up and down the tank flaring their fins to show off the white bands.
I'm very glad they are doing well as I still harbour some inner guilt for believing the shop (many years ago) when they told me they were good tank mates for goldfish