I have a mix of sand and mixed mixed at a ratio of 85:15, i.e. 85% sand 15% peat. The pH measured in 2:1 soil to water solution is 4.71. I'd like to adjust to pH of 6.5 but how much lime should I use? I don't have time to send away for a soil test and surely there must be a rule of thumb for how much lime to add to a given volume of mix like this. Any ideas?