Well, I've let the Al + HCl bath alone for a while and I think the brown sludge is AlO. What I reckon is happening is that the AlCl is attacking the oxide layer like NaOH does and the water in it is reacting with the fresh Al underneath. Humm, might need to use less water and more HCl.
Another thing I've seen, I may have said it before, is that there is also a sky blue and green stuff mixed in with the brown sludge. I wonder what it is? Magensium perhaps? I know they alloy Al and Mg together for use in coke cans.