Total Watts (equipment) divided by volts (120) = AMPS
Total Amperage on a single circuit should not exceed 80% of listed amperage on the breaker (15 amp = 12 - 20amp = 16). This is total for a circuit, not just the fish tank!
Wire gauge 15 amp = 14 gauge wire. 20 amp = 12 gauge.
DO NOT PUT A 20...