Well, finally made the rest of the journey, the goal posts kept moving due to viewing it on different platforms, so page numbering was all over the shop causing an awful lot of revisits. I got there though, so im up to date.
If this is due to dreaming & forking out some green more than pure explicit planning, then i say it equates to the same outcomes. An evolving multifaceted project that has you hooked...... & by the look of comments along the way, the rest of us as well.
Your water level looks far superior at these levels. Keeping it there as you mentioned is a hassle till you find the leak source. Perhaps a combination of things besides the usual evap & diffusion. If you cant lock it down, my only suggestion would be to grab a moisture probe and benchmark the perimeters. Given the lay of the land, you would know what your expecting before long.
If your looking to spend any more money in the future, try looking at a liquid nanotech SiO2 layering product. In a spray-able form, it might potentially assist in a whole host of applications regarding your project.
The choices, & sometimes experimental planting, the greenage tug of war headaches, wildlife gatherings in some Costa Rican field of dreams, or the evolutionary build focus - these all pail in light of those select handfuls of shots of your family being met & frolicsome with the aquatic inhabitancy. This is the dream realised. Well done bud.
Although i did notice, not one test result of any kind?
*In Edit* I was also thinking about your earthworm problem. Given a course mulch, would that allow them to transverse the surface, yet not try to go higher?