OK, so one of the cottages where i work has either a 55 or 75 tank. i'm not sure which, i am thinking by the size it's 75. anyway, they are running one emperor 400 on the tank... and water is literally JUST trickling out of the outputs. BARELY even enough to keep the biowheels spinning. i have adjusted the spray bars, checked the empeller, and entire assembly (short of the motor). i use an aquaclear myself, so i don't know much about it. as far as i know this filter is only about 4 months old. there are 4 cartridges in place... all new. i took two out to try and increase output... no such luck. it just seems like it's not taking in enough water to maintain the level needed in the filter. it's been making the "priming" sound off and on as well. am i missing something or is this just a bad filter? this tank houses maybe 20 small tropicals and one HUGE common pleco. the tank is getting so nasty because the pleco poo alone piles up on itself. the filter is just NOT sufficient. period. my filter on my 10 gal tank puts out more water than this thing is. i've pleaded to get money to buy two AC 110's... but i don't think i'll have much luck. if anyone has any advice, please let me know.
thanks.

Have you cleaned the intake pipe? It could be that it is almost clogged.

On my Penguin if I don't clean out the little holes for the biowheel to sit in every two weeks, then the plastic wears down and starts to slow down the spinning.

You said you cleaned the impeller, and I know that has caused problems for me in the past, everything getting slowed down because there was just too much gunk in there.

the filter itself really wasn't all that dirty. heck, my AC was dirtier than it was, and it's only about a month and a half old. i just don't know what to do about this one. i couldn't believe it was running as it was.

Emperor's are kind of tricky at times.If you're changing out water,and the level drops too low,you usually end up with that onnoxious priming/grinding sound.It once took me two weeks to get one to sound normal again. If you've checked,and all the "flow areas" are unclogged,and the filter's themselves aren't completely gunked up,then I'd go back to the beginning.
What I did was I got a large pitcher filled with tank water,and as I poured it into the filter box,I also continuously lifted the intake tube ,placeing it in, then out, then into the impeller box over and over again.It's almost like the filter has to catch a large amount of water at one time,in order to stop the noise,and if that intake tube is even off a tad off,it won't flow right.It's really hard to explain just what I mean,so I hope that you're getting some idea. I would find an hour of free time and give this a shot as it sounds exactly what I've been through before. I think that I have 6 or 7 of them now,and have learned the Do's and Don'ts about them.

I think Sharon may have put her finger right on the problem....

Emperors are WONDERFUL filters. They do seem to vary a bit - some will almost self prime, given a bit of water in the filter box, and others need constant water being poured into the box while they are starting up, to get them to go.

The main problem, though with them is that many of them (not all) are incredibly sensitive to water level. If I try to run an Emperor on a Rubbermaid tub where the water level is about 2 inche below the outflow level, it will have trouble starting, make horrid noises and only trickle....

Try raising the water level in the tank so that it is even or barely under the level of the outflow. I bet it improves the filter quite a bit.

(The filter should have 2 clam shells of media and two cartridges)

well that may very well be the case. i was told they do keep the water level down (more than i would) because of the splash back when the water hits. they have a wooden hood and inside are two strips of glass placed over the tank that the light strip sits on. anyway, i will try my best to get down to that cottage and fiddle with it asap. i hav a funeral to deal with now, but i will try your suggestions. thanks a bunch!

All of my filters are of that type, and it's kind of a pain when the water slows down that much.

Usually if I clean the intake basket very well and clean out the little motor assembly well, that will take care of it. Especially if the grinding/priming sound keeps happening, I have a something small caught in the filter, or the water level is too low for it.

If there's other aeration in the tank, you can also just fill it up higher, so the return lip is underwater and you won't get any splashing that way, which is what I usually do.