1ST. I HOPE U GOT THE HYDRO TRIO AND NOT THE SOIL TRIO. i sure hope u get it figured out.
when did your plants change from healthy looking to what you show in pictures ? had u made any changes u recall during that time just before the visible. hydro reacts to variations and changes pretty fast.
Old man river gave u good advice.
if you get through this i suggest you go to soil because it's what you know and is much more forgiving. then u can easily transition to soiless then coco coir or hempy buckets for the most simply hydro u can do.
easier to learn that way imho on your way to being a master grower or at least expert. ijs :)
make sure u review the meters well before you buy and check growers who have used the ones you have on your list. warranty, calibration, accuracy and durability are key buying point imho.
i ended up getting a truncheon like 10 years ago, simple and cost effective. i need to find out too cause i haven't seen them for sale. i guess it would help if i could recall who made it lol. i do know who i brought it from so maybe i can check them. back then blue lab was the standard but frankly it was overpriced. ijs
this company sold it but have reduced their line over the years and i'm guessing the one i brought didn't have a high enough profit margin cause it sure as hell worked and did all this blue lab truncheon did very easily. they had s standard one and also a digital one. i brought the standard and it was easy. damn i need to find it now my OCD has kicked in. smdh
https://www.nehydro.com/ph-tds-testing/tds-ec-meters/bluelab-truncheon/