Seedling is the most important starting material for muskmelon production. Healthy seedling production can be addressed by finding appropriate seedling substrates. Blue crab shell powder (BCSP) has been used as a substrate additive to increase the growth and yield of agricultural produce. This research aimed to investigate the impact of using BCSP on the alteration of EC, pH, leaf greenness, and growth of Cucumis melo var. Hamigua TA215 seedlings. The substrates making up the treatments were 5, 10, and 15% BCSP, and peat moss was used as a control. Four treatments replicated three times were laid out in a Completely Randomized Design (CRD). The results showed that increasing EC and pH were attributed by increasing the BCSP. After 9 days of watering, a reduction of EC was found. On the contrary, pH in 15% BCSP adding treatment was gradually increased and reached the highest point at day 9. Alteration of EC and pH affected leaf greenness. The highest point of leaf greenness was found on day 1, consistent with increasing EC. Final growth was most significant for seedlings grown in peat moss (control) and tended to decrease as the percent BCSP increased. These are indicative that essential elements in BCSP resulted in leaf greenness appearance. It was growing of pH impact growths of seedlings. Reduction of the amount of BCSP might provide favorable conditions around root environments for the seedling development of muskmelon with healthy growth.