By lime I mean gardening lime. It comes in three forms. Hydrated or pulverized powder type lime acts the fastest to raise PH. Dolimite type lime works a bit slower but lasts longer and is easier to spread over a large area with a spreader. It also has other nutrients. Pelletized lime is in between and is basicly hydrated type lime formed into pellets. For this purpose I suggest the pulverized powder type for quickest results. Just rake it lighlty into the top 1-2 inches. If it's like PH 6.5 or lower add about 1 lb (2 cups) to a 3X6 area. If its like below 6.0 or lower, add 2 lbs for a 3X6. These measurements are just rough estimates and your soil conditions may require different amounts. Test it again in 6 weeks and add more if needed. I am not sure about the meter you mention, but get a gardening type PH meter or kit at a garden store to test your soil. Don't worry about testing the river water. It is unlikely that it would be so high or so low as to adversly affect your plan't growth if you water with it. .