<p>Gracilarioids species (Gracilariaceae) are economically viable options for aquaculture in Brazil. High-quality seedlings produced through vegetative propagation are essential to reduce pressure on natural beds and can be achieved in controlled environments. Commercial fertilizers are low-cost effective options to improve growth and quality. Additionally, CO₂ sequestration can add further value to their cultivation. This study aimed to analyze the biomass production and CO₂ sequestration of <i>Gracilariopsis tenuifrons</i> (C.J. Bird &amp; E.C. Oliveira) Fredericq &amp; Hommersand under two concentrations of a low-cost commercial fertilizer. Growth, pigment content, dry biomass proportion, and C, H, and N contents, along with CO₂ sequestration, were measured. <i>Gracilariopsis tenuifrons</i> was cultivated for 28&#xa0;days under two concentrations of a commercial orchid fertilizer, Forth 30–10-10 (NPK), one with 250&#xa0;µM of N (referred to as 50%) and the other with 500&#xa0;µM of N (referred to as 100%). No significant differences in growth or growth rate were observed between the 50% and 100% treatments, with a maximum 4.4-fold biomass increase by the end of the experiment. However, significant increases in phycobiliprotein and N concentrations were observed, with the Forth 100% samples showing 33% and 20% higher levels, respectively. The C content was higher in the Forth 50% samples, with a CO₂ sequestration rate of 14.8% per unit of fresh mass. <i>Gracilariopsis tenuifrons</i> demonstrated a CO₂ sequestration rate comparable to that of other macroalgae species, highlighting its potential for cultivation. Moreover, greater biomass production and CO₂ capture could be achieved by combining nutrient addition with increased light exposure to boost photosynthesis and growth.</p>