I had the Emperor 400 on my 55 gallon. Very reliable, a bit noisy, but excellent at keeping ammonia low. There's plenty of reviews on this filter, but I'm surprised no one mentions the pair of gray plastic inserts that allow you to choose your own media. I actually found that they were a pain. Difficult to close with media. It's almost impossible to fill them without being able to see right through them. It's great in concept, but poor in execution. I switched to an Aquaclear, simply so that I can more easily try various media alternatives without the hassle. Nevertheless, this filter was very reliable and capable of handling a decent bioload.

My first Emperor 400 is still in operation after 9 years. It has seen a host of other filters to accompany it and it keeps on going and doing what other filters only dream about. There are very few products that I feel this way about, but without spending large sums of money, you will not find a better filter. My only complaint however is the replacement cartridges. I have a huge pile of carbon in the bottom of the box. I really need the carbon in the cartridge. Please tell Marineland if you to have this problem. I guess everything can not be perfect.

tank stays clear all the time.

I originaly reviewed the Emperor 400 in 10/05. Since then it no longer has the flow control lever. so you cannot decrease flow when feeding and it no longer has the viewing windows to make sure the biowheels are turning. I emailed Marineland and they eliminated the flow control to decrease noise ?...Also they didn't say why they eliminated the biowheel view windows( my biowheels have stuck on several ocassions)also it now has a mid-flow intake which is silly..I think they did it to save a few cents on cost..I will now buy Aquaclears when I need my next filter...Cichlid forum should update there product description to eliminate flow controls...

I have had the same emp 400 running for 7 years and have only changed one impellor. I have made a few modifications and now this little filter is the sole mechanical filtration in my overstocked 125 gallon aquarium.

The best HOB filter ever made. Keeps water extremely clean and works very hard.

I purchased an emperor 400 for a 29g tank a few years back and it has been an excellent filter.. The filter
cartridges are larger than most hob filters and I really like the media containers that come with the filter. The additional spray bar to insure the biowheels won't stop is a very nice feature as well.. Overall, I've been
extremely pleased with this filter.. Anyone considering a bio-wheel hob filter, look no
further..This is the best biowheel filter on the market.
It is a little too noisy for bedroom use but fine for other areas of my home. It's a great filter, second only to the Hagen Aquaclear line.

This is a truely effective filter for any aquarists. Some would argue the AC500 is superior but that's misleading. The only reason why you would want an AC500 is bcuz it's cheap. AC500 cost less and their media cost less. AC500 is not a bad filter but not as good as people claimed it to be. I believed the E400 is far more superior. Good flexible plastic which prevent breakage if you accidently step on it or drop the lid. Large bio wheels with water spray bar to propel the wheels, holds almost 1gal, adjustable flow control, can be quiet if you tune it which I will specify how later, and it has plenty room for extra media. Be creative with any media you might want to add. Not to mention the design is very sleek and attractive. Yes, the E-400 can be noisey due to the impeller design. It's a dual impeller which means it has two impeller spinning at the same time. The key is to keep this impellar as clean as possible and be anal about it. If a small grain of sand get caught in between the two impeller then the impeller will rattle making a loud roaring noise. This filter is not recommended for aquarists using sand substrate. DO NOT ALLOW ANY SAND IN THE FILTER OR ELSE YOU'LL SPEND A GREAT DEAL OF TIME CLEANING THE IMPELLER. Cleaning is not the easiest among other filters bcuz you sort of have to be handy to know how to take it apart with easy. I have a mechanic background so cleaning is not troublesome to me.

had a problem getting it to prime but after 6 hours running, water is polished and fish are all over the place , I've done my research on filters and this is the best one for the money . won't change to caniser filters cause owner of lfs said canister filter are inferior to emperor 400 cost me 49.99 at hidden reef.com

so many arguements on which is best AC or Emperors, my experience, Emperors are the best money can buy, AC are the best for the money, any question?

I started out using the 400 and i have tried others but i always go back to marineland...there just isnt a better HOB out there...

My 1st aquarium was in 1971. I've used the corner, underground, and HOB filters. I have 2, Emperor 400's on my 75 gallon. As others has stated the media choices are numerous. These filters come with two optional use slotted plastic holds to put any type of lose crystals, charcoal, etc. you perfer. I am very surprised to see some members are having problems with noise. I would also have to state the only noise both of mine make is simply the water flood back into the tank, which sounds a relaxing waterfall. I did have to do some initial adjustments to make sure there was no loss media, or loss contections with fittings during assembly.
My biggest advice on the Emperor would be cost on the box of 4 replacement filters that can run $17.99 and in my case that's times 2. I recently found a website that carries the name brand by Marineland for less then $9.00, a huge savings. I haven't ordered them yet, so I'm not so sure about S & H charges, but I still think it would be worth it.

Makes some noise, but not as bad as they say. And quieter if you keep the sand out of them. Huge bio-wheels, spray bars, customizable media trays, holds over 1 gallon of water. What more do you need? Best filter I've used yet.

I have used Emperor 280s and 400s. Both are noisier than the Penguins and AquaClears I have used. The spraybar is supposed to aerate the water and promote growth of nitrifying bacteria, but it also makes the filter very noisy.