A method of fluid treatment of a feed comprising oil and water, the method comprising: supplying the feed into a flotation cell, the feed having an oil concentration, the flotation cell containing a working fluid and the working fluid having a surface; removing an oil phase from the surface of the working fluid; removing fluid from the flotation cell through one or more outlets below a working fluid level in the flotation cell; and controlling flow through the one or more outlets to maintain the working fluid level in the flotation cell within a predetermined range independent of variations in the oil concentration of the feed. A related apparatus is also disclosed.