Those numbers dont surprise me in the slightest. Beyond the Abyzz and red dragon DC pump lines you wont find much in the way of head pressure handling in the typical chinese sourced DC designs. Not knocking those that use them, but lets think about things critically - there is a finite efficiency that can be squeezed from a given wattage input in the form of either flow or pressure. You cant look at a pump drawing 90w max for example and expect it to be as stout in the face of plumbing restrictions as one that pulls 180w. Even if the 90w max pump's box says it moves 2x the gph of the 180w pump. If you want closer to 800gph in your case, try a fluval SP6. The askoll made motor blocks and impellers are as efficient as nearly any DC pump in terms of gph/watt and way more reliable than anything else in the sub 300 dollar range.
DId you try changing the plumbing to 1.25” or 1.5”? I’m guessing the 1” plumbing is causing more head loss than your’re expecting.
Yup, I agree with that assessment for sure. In a lot of these prefabricated tank/plumbing setups I see situations where using a larger diameter return line up the the tank then splitting into 2 or more half inch outlets would vastly improve the flow vs. the narrowing of the single return line down to small diameter before it hits the aquarium. I like the velocity offered by a half inch return nozzle, but much prefer to run 1 inch or 1.5 inch line up to a T which the houses reducer bushings to step down into half inch locline. 2 x .5" nozzles can actually flow a decent amount if they are supplied with appropriate upstream piping and a pump with decent pressure. They are useless however if the line feeding them has already chewed up all the muscle the pump had to offer.
