New Haven Harbor watchers take note: the waterway is about to become home to two more large oil tanks. The new tanks also mean the storage capacity of Safety-Kleen, an oil recycling and environmental cleanup company, will increase to more than 6 million gallons. It brings the total number of tanks on the harbor and lower reaches of the rivers that feed it to about 115, according to an activist who has counted them. The two new, above-ground storage tanks, each 72 feet in diameter, will add capacity to store an additional 3.64 million gallons of used oil. That will raise Safety-Kleen’s on-site storage volume to 6.42 million gallons, representatives said. Safety-Kleen, based in Richardson, Texas, and founded in 1963 in Milwaukee, has been a subsidiary of Norwell, Mass.-based Clean Harbors Inc. since 2012.