Diversion at its simplest, make a Saddle Valve to bleed off excess.
Saddle Valve works and its probably the cheapest means of water diversion, however it do create quite a splash in the tank. How to make Saddle Valve : Here
Above photo water reduced on the delivery side of the pipe.
More common method above using ball valve on a "Tee" diverting water. Need additional item a "Tee" and a Valve, not that expensive just add more things to the shopping list.
Above an attempt to reduce the splash from Ball Valve outlet.
Just another way above to reduce the splash.
10 inches standpipe for a 12 inches growbed.. can be adjusted to what ever length by reducing length of extender tube.
Extender tube remove, above stand pipe is at its basic height of about 5.5 inches. Tested at both height no problem, now I test at this basic level because less time to wait.
What I practice on my growbed is high water level initially and I will reduce it once plants start to grow, its depend on what plant you grow some need more dry zone then others.