This study tended to evaluate threshold operation criteria of biostimulation for optimal biodecolorization in immobilized-cell systems (ICSs) using Porites corals as packing matrices. Indigenous Aeromonas hydrophila with high efficiency for decolorization isolated from Northeast Taiwan was used for study. As maximal treatment performance of ICS could only be achieved with maximal absorbed biomass with highest color removal capability. Maintaining optimal attached cells for cost-effective color removal efficiency inevitably required essential nutrients provided from rich media for biostimulation. With consideration of efficient cell attachment and maximal dye biodecolorization, our proposed method of "graphical reconstruction" quantitatively revealed the most economically-feasible strategy of medium stimulation for color removal. Our findings pointed out the maximal allowable inlet concentration and treatment capacity using our prediction of constant-slope isoclines of ICSs at cultures fed with different concentrations of nutrient sources. The method of isoclines upon transient dynamics of ICSs also provided a technically viable assessment for on-site professionals to quantitatively determine maximal biotreatment thresholds in biostimulation.