When I went to the store i looked at the meter you have and the guy said that is mainly used for soil dampness so you know when to water. if you notice, the more dry it is, it will read alkaline, no matter what the pH really is. get bottled water, and the liquid pH tester and all will be good. your plants do look good, so in reality you may not need to change a thing. rain water is "filtered" through the ozone/air and if there are pollutants, like in big cities, that will also be in the water.

i flush my plants more than most, but they seem to thrive, i would always flush them, especially soil, before going into flower. flushing your plant removes most of the extra salt built that is from what's left over that your plant can't use. when you flush, it's the closest thing to getting fresh soil without repotting. if your soil gets to much salt built up than the plants natural response is to "balance" itself with the soil and it actually starts rejecting nutes and showing defiencies.

also, to check the pH of your soil, know the pH of your water and then check the drainage. adjust as nessecary. if it's below 6 or above 7 then you can start running into problems. with bottled water, it should be pretty neutral. i said vinager because it's something most people already have and i know someone who uses it with little to no effect on the plants.