well, a couple things come to mind. Have you cleaned the rio yet? If not now might be a good time to do so. And whe doing this, there are two small grey plastic elbows on the intake of the pump that are connected to air hoses, ditch em'. they clog with salt creep very quickly and significantly impact performance. Secondly, after that is done, play around with the green valve. start off with it all the way open (Take it completely off) and let it run for a couple minutes. it will be noisy, but only until you put the valve back in. Then, put the valve back in and very gradually begin tightnening the knob until the pitch of the sound changes from the pump. it sounds kinda strange, but you should hear what I am talking about. as soon as you hear it, back it off a touch and you should be all set. This is how I set mine and mine pulls out a decent amount of stuff. Let me know what happens. if this doesnt fix it, there are a couple other things that we can try.
HTH