every meter is not the same. if you use rain water or ro water (reverse osmosis) your # will be sigifignantly lower because your water is lacking a lot of elements found in ground and city water. your plants don't need salt but it is in most municipal water. you need to read the starting point of your water to know where you stand, if it is to high use different water. in southington i have a ro system, the biggest problem is acumilated salts. do you ever flush your soil or grow medium to get rid of salts? plants don't like salts. there are some products that will help you flush your soil,medium but you can usually just run a lot of water through your medium to flush the system. the ppm meter system conversion sucks because they measure electrical conductivity and every element registers differently on everyones scale. do you have salt ,nitrogen,trace elements ect. thats why in hydroponics you change out the fluid because you don't know what the plants used and what is building up to a toxic level. flush you cant go wrong . don't let the plants drink the flushed water let it go whereever.