Hanna ORP Solution, 240 mV, 500ml YSI Meters Feature Specification Manufacturer Penn Plax® Model Clipboards Feature Specification Manufacturer Penn Plax® Model B11 Product Type Automatic Battery Back Up Air Pump Power Source 2 × D cell batteries (not included) AC Connection Detects power outages only (does not power or charge the pump) Automatic Operation Yes Manual Operation Yes Maximum Aquarium Size Up to 55 gallons (208 L) Operating Time Up to 48 hours (depending on battery quality) Air Outlet Single Dimensions Approximately 6 × 3 Product Code: 2424 B55 specifications indicate that the electrode reading should be within approximately ±20 mV of the nominal value Supplied in a 500 mL bottle