Alright, since you have a baseline (a years worth of previous history on this filter) you'll be able to see quickly how the changes effected it.
I trust the discolored material is the old stuff used to 'seed' the new filter.
Mattress foam padding can channel water if you lay it flat, make it dish shaped so the weight of the water pushes the water thru it. It will get a little disgusting around the edges that are out of the water from water creep, but no harm.
Aeration would help your system (filter), but the way you have it set up I'm afraid it will condense under your top filter material to one big bubble and 'burp' moving the material to one side and screwing up everything. Will work ok if you put egg crate (plastic) on top to hold it flat.
How's the inline filter holding up (have you tested the water quality coming out verses going in)?
Did you ignore my question about the 'other ' filter??
Keep up the good work, it gives encouragement to others to know they can try too, you've come a long way (still don't know why DGF stays, she must like being ignored
).
If Home Depot and Lowes carried fish, all the LFS's would go out of business!
Looking forward to your posts,
Dr Joe
.