How do you guys lower the pH of a 60 gallons tank? I use R.O water but the pH is still high like 7.2-7.4, and if I want to lower it to 6.6-6.8, that would take a lot of pH Down. A bottle of pH Down cost $4.50. Is there a cheaper alternative such as buying large quantity of H2SO4? Where to buy? Thanks for any help.