Stop doing anything to your water besides "aerating" it for 24 hours before using it so the pH can settle.
Without a specific reason , there is no reason to adjust your water ,and if so Ph is not the thing.
Your gh and kh are fine for most things and certainly for your platy.
They are more important then pH and as mentioned Kh is what stabilizes pH.
Seachem makes great products.
Stay away from all that are meant to adjust your water!
Your fish will appreciate the water being the same more then you struggling to make it perfect.