This is a replacement part, not an entire unit! Optimize nutrient strength during growth, flowering, and fruiting Same reliable waterproof dustproof housing as pHTestr. Choose from models for TDS or conductivity (ECTestr); 1% accuracy. Replacement sensors and solutions OK-35661-17 for TDSTestr Low, High, ECTestr High OK-35653-13 15 mS calibration solution for High Testrs