Thanks for reporting those results. I would suggest/request that you try "washing" the board with etchant using a small piece of sponge.
I've tried that, using a soft amber colored plastic (polyethylene?) foam sponge and it seems to work maybe twice as fast as the sloshing method.Message
Re: [Homebrew_PCBs] Experiments with ultrasonics and vibration etching
2013-10-20 by Jan Kok