I searched on the net and found out that:

Design mix for M5 is 1:5:10 (1-cement 5-sand 10-Coarse aggregates) so if that's the case: Than find the volume of pouring in the pool.

**The amount of cement used will be:**

Amount of cement (in cu.ft) = (Total Volume of Pour x ratio of cement used in the design) / Sum of ratios of aggregates (fine and coarser ones)

1 bag of Cement = 1.25 cubic feet

No. of cement bags to be used = Amount of cement (in cu.ft) / 1.25