For eventual incorporation into a general theory of phytoplankton dynamics, an equation for gross daily production in a water column is needed which is an explicit function of phytoplankton concentration and which does not contain parameters or coefficients de- pendent on phytoplankton concentration: the production equations of Steele, of Vollen- weider, and of Fee are transformed to meet this requirement. It is also desirable, in order to simplify theoretical analysis, that the parameters in production equations be chosen so as to minimize the range of values needed to describe the variation of photosynthesis in nature. This can be achieved by choosing the quantum yield of photosynthesis in weak light as parameter instead of the maximum rate in saturating light. In lakes, the value of the quantum yield in weak light is likely to be about 0.06 moles carbon per einstein absorbed. An additional advantage of the transformed equations is to make evident a simple relation between actual daily production and the upper limit to production.