Green pool water in mexico

[prop]

i`m in southern mexico and have a pretty big pool ,120,000 liters.it has been no problem since we first built it 6 years ago.problem is with the water supply this year.many people are having the same problem.the water we get from the city comes on 3 times a week and people fill thier systerms and storage tanks.the water comes from a local well or river.we are on the ocean and at sea level,don`t know if that matters.this year the water has been turning pools green and brown.i don`t think it`s algae and have heard it`s phosphates or different metals.i do know that when i add chlorine ie gets worse.i have used a clarifier and then vacum to waste the residue but then need to add more water .i have a well also and the water from it doesn`t seem to make much difference.even if i run it through a cartridge filter first.i did fill it all the way up and then wasted out the residue and that seems to work but still have to add water at some point.i ordered d.e. and started to add that to my sand filter but it doesn`t seem to help much.there are a couple of pool supply stores here but not alot choice on chemicals.any help would be greatly appreciated thanks.