I got tired of the GH drops. They suck if you run multiple reservoirs and if you do a morning, afternoon and evening test, it adds up over the years. I bought a Bluelab Combo Meter off Amazon for a little over $200 recently. The Bluelab pens are $110 anyway, so for another $100 you get PPM/EC and the same replaceable PH probe as the Guardian. It’s battery powered, which I really like. I leave it in a res for storage and pull it out 3-4 times a day to do my checks.