4 in 1 Digital Water Quality Tester - TDS/EC/Temperature（°C/°F）TDS Meter | 0-9999 ppm | Accurate and Professional for Drinking Water, Hydroponics, Aquariums, RO Systems, Pool （2025 NEW）

Whats your water PH and whats your runoff ph? How much nutrients are you feeding them? I'm having a similar issue (week 7 of flower). I checked my EC and TDS, then stopped feeding all nutrients. Then just alternated recharge and plain water, and finally weeks later the numbers are dropping. I'm running an organic grow btw. $6.44 for an ec pen even if it's not 100% accurate it'll give you an idea https://www.amazon.com/dp/B0F5BNZ4CP