What really puzzles me is where you found the patience necessary to subject the Al-sludge to gravity filtration :) . I mean, I am known as a very calm and patient personality, but that would just be over the line.
A little tip: use celite for your vacuum filtration. You can read more about it Post 384725 (https://www.thevespiary.org/talk/index.php?topic=9721.msg38472500#msg38472500)
(Chromic: "Celite", Methods Discourse). Better luck next time ;) .