I personally hate the test strips. I always have this doubt and I hate that feeling. I have em as back ups cause they are cheap and do work.
at least get the strips, but one thing to remember w. them testers. You also need to buy calibration solution ... probe solution....When I first got mine, 28$ ..I walked out with 30$ in fucking bottles, small bottles to add! I reuse my solutions and change them out every so ofter. I didnt wanna contaminate the whole bottle, So i pour a little into another container and use outta that.
I use a Flora 3 part, never had a problem w/ cal-mag. The micro formula is pretty good. Thats why I like three part hyrdro nutes...If i see a def. I just bump one of the numbers to fix. Aint got that power with all in ones...and most all in ones cant put some micro's in the mixmwith out making a imbalance and actually causing lockout. So some nutrients, especially all in ones Might need a different product to supplement some micro nutes. And a Cal-Mag bottle from botanicare is cheap and every grower should have a cal-mag source laying around for emergencies LOL