Okay, here's the thing.
I have just recently ventured into the wonderful (at least I am hoping it will become wonderful) world of hydroponics
I have seen lots of pH test meters and calibration solutions but I am confused on the whole pH 4- pH 7
and any other pH whatever. What is the difference in all of these?
hanna, blue labs Milwaukee and a few others. they are all about the same. Do not get one from the hydro shop, find on amazon or elsewhere. the 4.0 and 7.0 are calibration solutions used to set up and recalibrate the meter to know if its reading proper. Some will read the cal. solutions slightly different. you will have to check with manuf. specs as to which is the right one to use.
Super easy. hydro is easy. There is just a very steep learning curve. good luck hope this helps.
keep in a range of 5.8-6.1 and you will be seeing trees in no time.