Well the gph for all filters is with no media, no head height and no hoses at all. Just the pump itself. Now add in all your media baskets, media, floss, hose lengths, hose bends and turns you lose 50-60% of your pump volume. This assuming your impeller is in good working order. So you are right on track.
For your 17 gallon tank, you are fine.
Last edited by Somefishguy; 08-02-2020 at 12:32 AM.