In freshwaters, it is increasingly recognized that elements other than nitrogen (N) and phosphorus (P) are important drivers of productivity, community composition, and biochemical cycling. Much of our understanding about how elemental availability constrains ecological structure and function through limitation is derived from experiments and models focused on N and P. Those models are incomplete when applied to the 20+ elements that are essential for life due to unique chemistry and biological role of those other elements. Here, we’ll review existing models of co-limitation and limitation written in regards to N and P and how those models can be applied to other essential elements. Drawing from a series of trace element fertilization experiments, we’ll show how other essential metals, along with N and P, can frequently limit or co-limit algal biomass in streams. Examples from the literature will demonstrate how supplemental measurements besides just a biomass response (e.g., community composition, ecoenzymes) can provide a deeper understanding of ecological mechanisms that lead to co-limitation of other essential elements. Finally, we’ll discuss the suite of essential elements that can also be toxic when organisms are exposed to high concentrations. We will discuss advances in subsidy–stress theory, which can be used to describe biological responses across a wide concentration range, from limiting to toxic. We will share new synthetic work demonstrating how stoichiometric models of nutrient limitation can be combined with dose–response toxicity models to fit organismal responses across subsidy–stress gradients. Overall, advances in our understanding of essential element effects on stream organisms can be made through a broader use of nutrient limitation models that account for co-limitation, can link to nutrient availability, and work across broad concentration ranges.