Homebrew PCBs

For some reason this didn't get posted last week, my apologies if it shows
up twice, but I'm making boards on Wednesday, and would like some input.

In my Kepro datasheet, it says I can shock the solution by adding some spent
Sodium Persulfate so I don't have to wait for it to stabilize.

I had some used solution which was 3 months old that I used to shock the
bath. I know the shelf life for etching is 3 weeks, but can it still be used
to add in adjusting the pH? The experience as shown below seemed to indicate
its not possible, but I want to know if I need to look at some other reason
for the slow etch rate.

I went ahead and etched, but it took forever. I was successful at 12/12, but
the etching seem to take 15 - 20 minutes. When I had my techs making proto
boards, it seemed we could etch in 2-4 minutes. The solution was at 105-110
deg F. The board was quite small, and as I use huge ground planes and leave
dead copper on the board to reduce waste, It seems it should have etched
close to the 2 minute time frame rather than 20 minutes.

 I doing tray etching with manual agitation.

Thanks
Ron