Help setting up sump

[koby325]

I have a 75 gallon mixed reef and im setting up a 29 gallon sump for it. How much space should i leave at the top of the sump so that i wont overflow it if i lose power.

 

[Saltwatercoral2]

I like to leave about 5 inches of room from the top of the baffles to top of the tank but thats just me.

 

[koby325]

thats what i was thinking 4 or so inches