Sand doesn't cause algae. You need to keep up with water change, lightly substrate vacuum (use a turkey baster, for details watch the video of 2hrAquarist "water change the 2hr way")
Check CO2 if it's still enough.
If the algae are returning (means that you have beat them before), means that:
1) plants mass increased, so you need to dose more CO2 or start trimming plants
2) as plant mass increase, you need to increase more ferts (or trim plants)
3) maybe you have increased light, without increasing CO2
4) you skipped WC or didn't perform any vacuum of the substrate.
The sand can't cause algae. Masterline purity isn't needed (using it will not hurts anything but I used months ago Seachem purigen, now I've removed it from the filters, and the plants started pearling way more)
If I'm not wrong, you use ada Amazonia? If you moved a lot the aquasoil, it leech nutrients in water column, this can cause algae that can be easily resolved with 2 50% WC weekly.
About "anti calcare" what would do with it?
Everytime you disturb too much the substrate, an algae bloom will appear, if you move the substrate (uprooting, vacuuming) you need to perform WC at the same time