You obviously have moisture getting into an exterior block wall.
It may be even worse because it sounds as if this wall is not
facing a conditioned space. Water alone will not harm the block.
If you live where it freezes, the ice will break the block. The
green algae will probably not harm the block.
The best thing would be to dig up the outside and waterproof. If
your area drain is working, I think I would poke a hole in the
bottom cells to let standing water out and a discreet hole above
grade to encourage air movement. I would guess that the block is
painted and sealed up for it to be holding water.
Keep the whole world singing . . . .
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