Well, I will tell you what. Most of thsoe meters come from the factory calibrated but they dont stay that way. All you need to do is get a small bottle of calibrating solution, the one that has the 1500 reading. Put your probe in it and there is a small screw someplace on your meter you will adjust until your meter reads 1500. Same for the PH meter. There is a two solution test kit and recalibrate kit for these. One is 4.01 and the other is 7.01 Starting with the 4, you put your probe in and turn the little screw until it reads 4.0. If you are using a multi meter, that is a digital meter with the PH and TDS on the same meter, there will be two sets of these screws, one for PH and one for TDS. To answer your question, yes, I have used them. What is it that you are using right now, the Bio Grow, Bio Bloom, Root Juice, Alg-A-Mix, Top Max or the Buzz Off? All are good but they also all have different applications so you need to be careful with them. I would go for the adjustment. I think that is about as close to your particular problem as we are going to get. You need to have the ps around 1.5 which is 1500 and the PH when using these ferts MUST be maintained at 6.