It's been a long long time since I took out my dusty test kits, but for one reason and another, I tested KH and GH today. While the GH is around 8-9, the KH is 0! pH is 6.5. Before I started using CO2 (currently just the Nutrafin kits) both KH and GH were quite high, and pH hovered around the 7.2-7.5 mark. Low KH has never been a problem I've had to deal with. :? What do I do?! All advice gratefully received as ever!