v=length times width times height
wait, we need it in yards
3ft=1yard
so height=1
v=45 times 30 times 1
v=1350 cubic yards
1 cubic yard=201.974 gallons
so times both sides by 1350
272664.9 gallons
per every 5000 gallons of water we have 1 of chlorine
so 272664.9/5000=54.53298
so we need about 54.5 gallons or 55 gallons of cholrine