you need a pH meter specifically for water. Hanna has a cheap one and have seen many other who post here use Hanna. I think its like $33 usdso im about to buy some supplies tomorrow and i can only get a ph soil meter not one that checks the water.. also im getting ph up and down. is the soil meter still good or....
this is the one i was referring toi paid around £6($10) for a tester that does soil and water, it also tests for moisture. works fine. got it outta my local garden centre.