drainage problems

I have a homemade flood drain table that is made out of a 3x3 planter with two one inch holes drilled into it.With 3/4x1/2 inch reducers syliconed into place one to flood the table and one to drain. the drain is hooked up to another 3/4x1/2 reducer at the bottom of a 10 gallon resivor and the other to a 170 gph submersible water pump both with 1/2 inch tubing.whin I fill my resivor up and plug in my pump the planter completely fills to the top and overflows what should I do about this I thought about adding another drain hole but I dont know?

turn the timer back to where it shuts off when its 3/4 or so to the top of the table

my timer will only let me set every 15 minutes.

get a timer that has more adjustments or put a new drain in but dont make it so big that the pump wont fill up the table

can i put two drain holes in?

Yeah I dont see why not just dont go overboard becuase you do want it to fill the table up, so start small and test it until you get the right size so the table fills up but not over flows

Get a smaller pump.