I will probably be getting another 12000 to run both at a lower setting soon.
These pumps feed slowly. I haven't started mine enough times to see if there's anyway to bypass the feed, but that won't work if it always does that. There's a feed button, but I'm not really sure how or when to use it. If they always ramp up to the power level you have them set at, then checking the sump level like that won't work.
They do have a build up time and there is no bypass afaik. The feed button is for feeding your fish without blowing floating stuff everywhere.