it works fantastic. The water in my tank was a little ...
934133
Took a while to prime this.  Wasn't syphoning the water but, after cutting the tubes to as short as required, it works fantastic.  The water in my tank was a little muddy (green) to begin with and after a few hours it was crystal clean.  The instructions are badly translated into English (Engrish) so I would highly recommend watching some youtube videos on how to set this up and maintain it.
4020497
It works really well. It takes a while for the water to be clear and not with air in it. Be sure you don't over tighten it.
300036
You know, I debated if I should invest in a more powerful unit or not but I have no regrets with this purchase.  After my original one died I was researching various pumps but found this at a fantastic price so had to jump onto it.  After some minor plumbing work and basice cleaning of the tank, I dropped this in and let it do it's job.  I don't know what the original unit was rated at (too dirty/rusty to tell and was here when we moved in) but this definitely pumps out more water than the original we had.  Honestly, my only complaint is the float.  Where it's set from the factory, it tends to turn on quickly but leave a fair bit of water in the tank.  It's not really a bad thing I guess, plus the switch is completely independent.  Should it go bad, just clip a few zip ties on the top and you can remove it (or adjust it if need be).
3054878
I had the problem of the black water tank sensor always showing the tank as half full, even after completely draining it.  After using this gadget just two times, the sensor is now displaying accurately.  I highly recommend this product, as it's paid for itself already.  I didn't experience any of the leakage problems around the valve that others have reported, so no issues there.
1268733
Before dropping the money for the Aquatop CF400, I was using a bio wheel Marineland filter. The bio wheel was doing OK, however, when upgrading to my 75 gallon tank it was struggling to keep up. Upon receiving the Aquatop as well as setting it up, the water was pretty good and I thought pretty clear, 24 hours later GOOD LORD!!! I wasn't sure there was water even in the tank. It was so crystal clear it was unbelievable, this thing was making the fish tank water just as clear as my water purifier does my drinking water (not saying I'm gonna drink my fish tank water but you get the idea):)only annoying part was the countless priming you have to put in to make it ready, but after seeing it in action it was well worth the priming and the money.
4780796
I've been using this for about a year now. I've had no issues out of it and I got it for a 10gl tank intentionally, just had to put a little bit of plastic around the bottom to decrease the excessive pull, but the fish I have in the tank is enjoying the constant stream of refreshed water.
3936709
I installed this filter in my 55 gal tank that is 2/3 full and has a turtle in it. The water was very mucky because my other filter had basically quit working. When I woke up this morning my tank was clean and clear. So, I love the filtration process.
Will wait a few weeks and see how I like having to completely disconnect and remove the filter for cleaning.
1343968
I got this tank 5 days ago, and it works beautifully!  Do not believe the negative reviews about how the tank came cracked.  I got mine and it was packed amazingly, and I cannot imagine anyone recieving theirs cracked.  In my tank I house a Betta Fish and a snail.  The filter is a little bit strong, but my fish has gotten used to it.  The lighting is amazing too!!
41731
So I'll admit it.  I laughed a little when I read the other review about the fish disappearing because they were sucked into the filter.  Boy do I have egg on my face now.

Yesterday I installed the power head in a 55 gallon tank for 2 large fancy-pants goldfish.  As soon as I installed it the fish perked up.  The venturi bubbles are awesome and the pump rapidly circulates water around the tank; this is what I wanted it for, to increase oxygen in the tank.

After work when I got home today I found my oranda stuck to the base of the filter.  Her eye is all puffy, and from what I've read I'm pretty lucky that she still has her eye intact.  I cut a hole in an aquarium filter sponge and covered the little suction dealie at the bottom.

So, even if you have large fish mind that serious suction!

Edit:  Haha, this review was written in bad taste.  The pump is still working great though, as of October 2012...
334282
This serves as my backup, second filter for my turtle tank, and it has been doing a fantastic job, especially since my penn plax canister filter stopped working on me a few days ago. it has been keeping my 50gallon with fish, painted turtle, and snails clear for the time being until i'm able to replace the canister filter.
1800360
It works great! The water runs out too soon though.
1849407
This float switch works great and is perfect for what I needed. I used this float switch along with a 1/4" 12v solenoid water valve and a 12v power supply to make an automatic top off filler for my 42 gallon aquarium. It works great. I ran a 1/4" plastic water line from my reverse osmosis filter in the basement and connected it to the valve which is controlled by this float switch. My filter system has a 3 gallon bladder tank on it so there is always a store of water under pressure which I also use for my refrigerator water and ice dispenser.

I love how this switch works for my super cheap homemade aquarium top off system. The nice thing is, I can siphon 2 gallons of water out of the aquarium every day or two in like 2 minutes and it automatically refills to the correct level without ever carrying water to the tank. I no longer have to do a weekly 20% change of 8 gallons and it's less stress on the fish. Plus, water evaporates quickly from the aquarium in the dry winter air, especially with our wood pellet stove in the room so with my automatic top off, i no longer have to add a gallon per day.
3294971
I was total dunce when it came to using this the first time. It took me a hot second to realize I had to submerge the ENTIRE thing in the water, then plug the hole with my thumb. After figuring it out though, it was perfect for my needs!
I am using it in a ten gallon aquarium, and though it takes a little longer than expected to clean the whole tank, it still works and gets the job done.
1925367
I bought this filter for my 46 gallon Bow front, I received it a couple of hours ago and it's been working great. It is easy to set up, The priming takes seconds, and It comes with media (carbon, ceramic rings, sponges). Overall I'm very happy with this filter, and I would definitely recommend it.
1607212
I was skeptical in purchasing this but decided that given how many people said that it controlled the water waste levels, for the low cost it was worth a shot. I was desperate to get the nitrite levels in my fish tank down for weeks and nothing was working. Just 24 hours after putting this in my tank and my ammonia levels are now 0 (previously closer .25+), nitrites are 0 (previously off the charts at 5+), and nitrates are staying between 20 and 40 (no significant change)! I couldn't be happier!! My poor fish even look happier. The tank even looks more clear than before. I'm just amazed! This package comes with it's own mesh media bag so just you can just put it in your filter and done. However, there is enough (according to the package) for 100 gallons. I was so worried for my fish I put the whole bag in my filter in hopes that it would work a miracle. But as my tank is only a 15 gallon, in the future I will probably either get the larger amount that comes in a closable container or get this but cut open the mesh and ration it out.
1635080
This thing works really well! The only down side is the capacity of the water tank, so make sure you don't want one slightly larger before purchasing. It usually takes the whole tank or a little more for a heavily wrinkled garment.
2041243
The Hw302 does an awesome job, and the price cant be beat. I bought this to help out my Fluval 306. I figured it would be good enough to add just a bit more filtration to my tank. I was pleasantly surprised though, I got way more bang for my buck. Plenty of room for your choice of filter media. It even comes with some media in the box. I used some of it, and added my own. The pump is pretty strong and seemed to prime right away. Definitely a great deal, so I won't waste time typing about how much I love it. I will instead point out things that weren't great, but definitely not deal breakers.

The instructions are horrible!! When they translated the instructions to English they used someone that barely spoke English themselves. Spending 10min. watching YouTube videos on this product fixes that. I cant stress enough how important this can be.
The Tubing is really hard. Routing the lines behind my tank were a pain, especially if your tank is up against a wall. I just kept telling myself, "You saved a ton of money, so shut it".
The media isn't the greatest, but it gets the job done until you can get better stuff. I did use some of it, mixed with media I had laying around.
Even with these small quirks, I do highly recommend this canister. Again, please take the time to research this on YouTube, you will be an expert on it before it even arrives at your door.