pump to small?

[mytank90]

i when and looked up size of pumps and after mesuring my mag 12 its smaller so thing its only a 9.5 i think.i have 2 90 elbows on my feed line to sump .first area of sump 17 inches wide then goes over /under /over glass to where return pump sits in area 6 inches wide bye 8 inches deep

[mark]

I'm with others, might be to do with volume.

To set level; with power on, fill display from sump until starts to overflow into sump, power off, let back flow until display stops draining, fill sump to the maximum level your comfortable with, mark max. Turn on pump, opening valve until until your drain flow max's out, mark water level in you sump say as max, power on. Your pump should be able to run without going dry to the 'max, power on' level, if not, your sump is too small. You can run your system below the 'max, power on' level to set heights for skimmer depth etc, not above.

With evaporation and not topping up (or having a ATO) you'll eventually draw air. With power on, never top up above the 'max, power on' mark.