System is working awesome, I am very pleased!
OMG the maintenance level has dropped to practically zero, plant growth has surged and enjoyment level is through the roof... woot woot!
I think I will add a layer of gravel to the bottom of the plant bin. Something like pea gravel I think, inert and not too small nor too large.
The small hose has stopped up a couple times due to bits of sphagnum that found their way to the hose. Good news is system still performed as expected. The pump feed became the drain and emptied the bin when timer cycled off.
Pea gravel should provide good protection against this. I am thinking just a modest layer... 1" maybe.
It will simply act as a mechanical filter.
I have also added an air stone to the reservoir, this should provide benefits on several levels IMHO.
One other operational observation, sometimes the priming starts a little earlier then expected.
As the drain sucks out the last bits of water some water bubbles are left in the hose. Then when the cycle restarts and the water level starts increasing in the bin the air pressure in the hose builds slightly between bin and the water bubble. At some point this increase in static pressure over comes the inertia of the water bubbles and they begin to flow, restarting the prime. This only occurs occasionally and doesnt seem to be an issue.
Not a concern nor a problem, just an interesting unexpected observation... It could be prevented by increasing drain hose size but dont see the need at this point. The benefits of the small hose size outweigh any small variance in bin water level.