The Biotek Marine Tek Series Sumps are of exceptional build quality and elegantly designed for the aquarist that desires the highest quality feature rich design. All Tek sumps include a probe holder which will hold up to 4 probes. The Tek probe holder adjusts as you adjust the height of the baffle wall so that the probe tips will always remain submerged at the same water level. Each Tek sump includes a heater bracket that secures your aquarium heater in the back of the sump. Measurements: Outside