Yes my PH trends acidic in both tanks and I bought PH UP from the pet shop at $20+ per 500g only to find its exactly the same ingredient as bi carb soda you cook with, at $5 a kg. My tank generally runs at 6.8 and adding a teaspoon every couple of days in my 600L tank trying to avoid spikes, I might visit pet shop and get some crushed coral or similar as suggested