1x630 15x42 2x315 18x35 3x210 21x30 5x126 6x105 7x90 9x70 10x63 14x45
Breaking it up into a rectangular and triangular prism, it is: 30*15*3 + 0.5*30*15*2 = 1800 cubic feet This converts to 13,465 US gallons, or 50,970 Litres. This is an approximation that assumes the water comes right to the brim of the pool, and that the floor of the pool is a constant diagonal. But it should be pretty accurate.
Why so many people find it so hard to calculate basic additives that they they all ask the same question, sometimes without key details so potential respondents can't help them anyway? First - what's "Shock & Swim"? It's no good quoting trade-names because anyone unfamiliar with it won't know its specific dose rate. Second - what do you mean, 15x42 "Easy Set" pool" Again, that's only any help to a fellow owner of the same pool. You should quote the water depth, or depths if it has deep & shallow ends, width & length, AND whether that's feet or metres. (I suspect feet here as 42m makes a very long pool for a private garden! 1) If you don't already know it, calculate the water volume in EITHER cubic feet OR cubic metres. That is basic school text-book or engineers'-handbook geometry. If using cu ft then multiply by the appropriate factor for US or UK Gallons. If using cu m then x by 1000 to obtain the litres. (1 cubic metre of water = 1000 litres) DO NOT MIX ft & galls with m & l. 2 ) Establish the existing concentration hence additive qty needed, by dip-strip or meter. 3) Now read the label on the disinfectant container or leaflet to establish the dose per so-many galls or litres. 4) Divide your pool's volume to find that "so-many" factor then multiply the dose rate by that, & adjust the answer to suit the existing concentration. . E.g. if your pool holds 50 000 litres & the instruction say "1kg of granules per 10 000 litres for 2ppm" then it's (50000 / 10000) x 1kg = 5kg for 2ppm rise. So if there are already 1ppm of bleach in the water, you need add only half that, i.e. 2.5kg, to give a new concentration of 2ppm. 5) last but not least... Now write down the water volume and the amounts of each additive & keep the notes in a safe place!