different kind of alginate salt gives different stability, so does the different grade product. The industrial grade alginate solution is more easily degraded by microbe in the air, because such products contain much algal particles and nitrogenous matter which offer plenty of nutrition for microbe. The pure sodium alginate solution can be kept at room temperature for several months without obvious change in viscosity. When temperature increases, all alginate solutions will depolymerize. Alginate solutions are stable in the pH range 5.5 – 10 at room temperature for a long time, but will form the gel below pH 5.5. Propylene glycol alginate solution is relatively stable at room temperature at pH 3–4, but it will lose the viscosity rapidly below pH 2 and above pH 6.