Review: SunSun 303B (HW-303B Canister Filter )


*Note* This review can be tied along to the SunSun/Aquatop Canister Filters. I've learned that both and pretty much the same unit besides the logo's slap onto the units themselves. (What I mean by this is SunSun 303B & Aquatop CF400UV are the same units! this hold true for 304B to CF500UV)

Ignore my horrible grammar. Worked a 12 hour shift, came home to clean fish tanks and then to hurry up and type this review!

The Canister Filter I'm doing the review on is the SunSun HW-303B Canister Filter. I've had this product in operation for over 2 months now, however this is my first canister filter I've owned. Let's start with the ratings that are advertised for the unit. The below paragraph is taken directly from

The Sun HW-303B external 4 stage canister filter is ideal for tanks up to 100 gallon. It handles up to 370 gallons per hour. The Sun HW-303B includes filter pads, hoses and all the parts you need to get started. The three flexible media trays allow you to add other filtration media such as Sun Sun's activated carbons, ceramic rings or bio-balls (each sold separately) to achieve excellent mechanical, chemical and biological filtration. A built in 9 Watt UV sterilizer helps control algae spores/bacteria and promotes clear water. The HW-303B canister filter also has a convenient self-priming pump that eliminates the need for manual siphoning

I'm skipping the unboxing part because to me that is unimportant, I'm after the meat and potatoes of the matter.

The first thing I noticed about the unit when it arrived was the amount of plastic used. Don't get me wrong plastic is good, but sometimes there’s low quality plastic getting thrown in. The base of the unit is made out of some very sturdy plastic; I suspect short drops, bumps. Kicks and other forms of minor to moderate abuse will not hurt the body of the filter. The bottom is made fully out of plastic but its good plastic with thickness on it

Moving on this filter model comes only with 3 trays (Please know how many trays the unit comes with changes with the models. All the way down to a low of 2 to a max of 4 **They also count the UV light as one of the stages of filtration**)

The trays yet again are made out of plastic, I've heard of people breaking them, but I find myself scratching my head as to how do you break them. There flexible, but as long as you don't crush, step or throw them like a dog bone I really don't see them breaking.(I've already filled my trays with media: Bottom tray all mechanical with coarse and fine filters, second tray Seachem Matrix and Purigen with fine filter and third tray Bioballs and more bio material with yet another fine filter. (The top tray has a plastic cover that goes over it, which all you do is keep lining the circles up.
I've also heard people marking there filters to know which way the trays go into the canister body but WAIT, If you look closely at the bottom of the filter there’s a circle! All you have to do is line the trays up with the circle and it will all go together very smoothly! But hey if you want to make a mark by all means go ahead.


Put all your trays into the canister body and now let's go look at the top of the canister! On the top there is a blue button (This is supposed to be the antI suck button) this button however great the ideal is not 100% fool proof. The button was a good ideal but it needs some tweaking done to it, but DON'T worry, see my tips and tricks at the end to help ya out. Also on top there is UV light switch that comes with a plastic cover, if you want to know if your UV light is on there is a small peep hole that will light up! There is also a hose connection area that I will go over in more detail later. (FYI the power cord is 3 pronged) See pics for more info!
Hopefully you’re still reading this! Yes I'm talking to you. Alright let’s flip the top over and take a look at the underside. Underside it where your UV bulb/Glass cover is located ***VERY IMPORRRANNNTTTTT WHEN DISASSEMBLING YOUR CANISTER *LIFT UP* DO NOT YANK SIDE TO SIDE OR ELSE YOUR RISK DAMAGING THE UV GLASS COVER***** If you break the glass you will not be able to use the unit until you get a replacement for it! You've been warned. The glass releases from it holds by a simple slider. Move the slider towards the impeller area and it will unlock the glass so you can pull it off. The impeller is hosed under a small cover that you need to twist to get it off. It takes a little bit of finger work but it will come off. See attached pics for more info!


Side note- The impellers above are 2 different ones, one is used on the 303B (Right) while the one of the left is used for the 304B. I tried to swap out the impeller for shiggles to see if I could increase the flow rate, however the 304B impeller is bigger and badder and refuses to work with the low life 303B.

Now let's go over the connection point where the hoses hook up to the main body. This part right here they did very well on. It's a simple valve that has a handle that you can lift up to cut off water flow into and out of the canister. When you put the handle in the up position it allows you to remove the hoses from the canister body itself so you can carry it away for cleaning. The valve is attached to a body that has 2 swivel elbows that are labeled In and out. They have full 360 degree rotation ability. Whenever you’re ready to reinstall the valve body onto your canister body make sure the handle is in the raised position then lower it into the slot and lower the handle and call it good. You will know it's seated well when it's flush with the body of filter. The way the connection is shaped there’s only one right way to insert it. If you somehow get it backwards I would like to hear how. See pics for more info of course!


I also added valves going into and out from my canister filter. The ID of the tubing is 5/8 in case you didn’t know; now you do! When I read this thing could put out 370GPH I was afraid for my fish getting blown away so I added a simple valve that would help regulate the flow.


After using the unit for an extended amount of time I decided to break it down and clean it. This is where most of the pictures came from. However before I took it apart I was curious to know if the filter was anywhere close to 370 GPH. I only had a 2 quart jug to use for testing. Everybody knows there’s 4 quarts in 1 gallon? I hope so. First time it filled the 2 quart jug in 13 seconds, double check my time 13 seconds again. 13 x 2=26 sec for 1 gallon there are 3600 seconds in an hour. 3600 divide by 26 gets you 138 GPH flow rate. Meh I was happy, plenty of flow for me (yes my valves where fully open). It's been 2 months since I cracked it open let's take a peek inside! (I should add I was using all the hose that came with the canister filter. The hose length is 6 feet long and yea I needed it all. It was pumping up to the top of a bookcase so it was about 6 feet worth of head pressure the pump had to overcome)

Let's just say I also aqua scapped my tank 6 times in the 2 months that I used this filter and it's showing the abuse I did to it. All 3 trays out covered in dirt, mud, and sludge. In the bottom of the canister body that’s pure sludge sitting at the bottom and yet this thing was able to produce 138GPH flow rate? I can't complain at all with that. On Aquadvisor it has the pump rated at 92.4GPH flow rate FYI.

. Easy to Clean, Easy to maintain, . UV Light (even though it's weak),.
. Plenty of tubing included in the box (I think it’s around 12Ft total),
. Prime Button!, Quick Disconnect of the hoses,
. Throw any media you want in it and call it good,
. Barley any pass through on particles,
. Good flow rate when dirty!!
. Nice and quiet in my room, it's about 6 feet from my bed

. The intake and outtake plastic pieces are cheap I mean cheap. Very easy to break, I did not break mine but that’s only because I realized how brittle it was.
. Protein Skimmer is not 100% functional due to the
cheapness. If you play around with your water levels you can get this function to work...took me awhile
. Instructions are nowhere what they need to be.

Overall: 8.5 outta 10!
I'm impressed out how this unit has performed for the amount of money I've spent on it. I wish the UV light was stronger, at the 9 watts it's currently putting out its only good for preventing green water. I would change the intake and outtake to something sturdier if you’re prone to breaking objects. Instructions are some of the worst I've seen, but I did my research beforehand and was able to complete the build with no major issues. Most issues came from the supplied Intake and outlet but yea they skimped on this to get the price down low.

I will rate again in a couple of months to see how long the unit has last. As of now I plan on buying the bigger unit the 304B and giving that a test run to see how good it is.

Taking apart the unit there are 4 latches. 2 which are attached to bottom and 2 for the top. You can use the 2 on the top to help you lift the canister top directly up without damaging the UV bulb but still be gentle.

Silicone lube will assist in making all the seals last/help you in putting the items together once you take it apart!

Hot water is your friend when you are dealing with the hoses. Don't be afraid to heat them up as this makes them more pliable making it easier to maneuver

Priming- Fill the canister body up with water first. Just enough to cover the top tray. Once that is done place your top on and connect your hoses. Then press the blue button a couple of times till water starts coming down. into the inlet and water starts going out of the outlet. Keep going until you get a nice stream of water going in. Once that is done plug it in. Your pump should take over now, just make sure water keeps going in. Once the water is going and you have a nice flow start tilting the canister around to help get the air bubbles out and watch it work. The unit will make loud noises will it attempts to get air out, that is why I tip it around to hurry up and accelerate the process.

Replacement-If you happen to break an item of the unit or need replacement seals the SunSun/Aquatop brotherhood is here to help you. Just match up the model numbers (304B is the equivalent of the CF500UV) between both companies and they both use the same parts.(Might be a slight color difference, but they both function like the other one)

My fishes thank you for reading this review and hopefully you enjoyed the review. If you have any questions please ask me or just reply back. I'm going to sleep now sorry for the bad grammar!
*Flow appears to have increased since I've cleaned filters but right now I'm too lazy to go measure it again! Maybe one of these days I'll get around to doing it again. The reason I say this is because the flow appears to be reaching into spots I have not seen before. Below is a sticker on the unit for info.

Remeasured GPH I averged 149 GPH, however some of my mechical filter is worn out also, so the more you pack the canister the lower your flow rate. Also warning If you have Neon Tetra that like to sleep near the intake you might want to make a wall to get them away from it. I lost 3 ever since I cleaned it. I wake up to find a few sucked up against the intake. I cut the power so they can swim away, some can but some can't....

The sound coming from the canister filter has increased in the past week, still not bad just a little added background noise, other than that as of right now still running strong

Update:Nov 15 2014, Hmmmm my wife checked the tank eariler today and the flow coming from the canister dropped. I'd say it was only about 50 GPH which had me extremly worried. Took apart the filter and found some of my mechanical media had disappered? and gunked up. Cleaned it all up again and retested GPH, I got 131 this time but I think the sponge I was using got trapped up into the head of the unit. I plan on taking it apart and cleaning it soon to see if I can increase that number. When I do that I plan on taking pictures along the way and showing what's inside.

Update: The breakdown happened awhile back, just forgot to post. No worries heres the story. I went on a short vacation....and came back to find most of my 40G water on my floor. At first I couldn't figure out what happened until I refilled the system and started turning everything back on. Checked for leaks on start up, didn't see anything initially came back an hour later and boom there's water on the floor. Looked around and found a stream of water between the body casing and top part. Took it apart, seal looked good, no cracks as far as I could see hmmm time to rip open the head. Sorry in advance for the bad pictures. If I realized they came out bad I would of took more before tossing the top in the trash.

The teardown after you remove the head from the unit, the screws are really easy to locate. If you can't locate the screws on your own, don't take the unit apart. This is only half the screws, but yea you get the ideal of what you are looking for, man sometimes I think I should of just did this on video .

The lid is now off! Do take not of the UV switch with the wires still connected. They are not screwed or crimped on it, just those slide terminal lugs that you can pull off. Takes a wee bit of force, but they do come off. If you

Now remove that blue antI suck button, under that button there's a collar which holds down a spring and the plunger like device the blue plastic cover sits on. see pictures below for additional visualization.

A couple of screws hold on the cylinder slide where the spring and coupling you just remove sat.
Remove that, the seal still looks good. Remove that and you can pull out two flapper doors. I did find some gunked up material stuck in there, not sure how it got there. These doors control the flow going into the pump. But wait.... why is there a hole in the back of my pump casing? I circled it in red. Its directly where in impeller goes.

Yea I bet you thought there was more to the tear down after the last set of pictures, but guess what that's it. Pretty simple yea, but I have a hole in the back of my pump casing and I know what your thinking. Its when I tried to swap the impellers out for a bigger one. I do like to experiment, but that one failed. Not really positive why that part blew out, but like all pumps its all sealed. So with sad news I must tell you ITS DEAD! (Died back in February of 2016) Well it ran good for the time period I had it, but its now 20160417 and I now have my sump set up with the KollerCraft TOM RP3 Overflow Box. I need to do a review on that. Until next time ladies and gentlemen I bid you farewell! I will have the other review up soon.

I FORGOT TO SAY all my fish survived, sometimes I'm so glad I have a planted tank, I think that's the reason all my fish stayed alive. My heater still works like a champ and the other additional filter added to the tank.. a little louder, but it still works. (Aqueon ProHeaters man those things are beastly and Aquaclear 110. Guessing both items ran dry for about 2 weeks while I was gone.)


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Very comprehensive review - the best kind! Thanks


Added info/corrected what spelling errors I could find. Reworked pics the links stopped working. (Let me know if this happens again and I'll fix it) Feel free to use this to whatever sites you fishaholics want or need. I just want the information to get out there.


Opened per request from OP


I cannot thank you enough for this informative post. Because of the information you provided I was able to repair my sunsun 404b. I had the same issue you described. When I took it apart there was a hole at the bottom of the impeller seat. This hole
was impossible to see unless the whole thing was taken apart. I covered the hole with epoxy and now I am back in business. Thank you! Btw, this was my first canister filter and I have made every mistake imaginable and likely more mistakes to come.

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