As far as HOB's go - I have never had anything but Aquaclear (for tanks that came with other HOB filters they usually only held one proprietary filter that needed changing monthly - no way to add additional media which is a BIG problem.
The bad news:
After nearly 4 years of owning about six Aquaclear ranging from the smallest to the largest size - I hate them. I REALLY hate them. If you happen to have live vegetation (especially floating) in your tank, you'll likely be cleaning the intake tube at least once or more daily. Over time they begin to warp so the lid won't stay on. It is RIDICULOUSLY difficult to get the intake assembly to fit in the space given, especially as the filter ages and warps - if there is a secret to it I haven't found it. Sometimes they just snap in perfectly the first time, but more often than not I find myself trying to find the perfect method to get it in place so that the tubing doesn't sit higher than the filter and you can get the semi-warped lid back on and have the tube suction from the impeller work properly. I find myself fighting up to 30 minutes or more with each intake assembly every week. I have messy fish, I tend to overfeed because I have species with diverse needs and I hate the thought of anybody missing out on a meal (my bad). For example, some are nothing but nocturnal algae eaters but many of the other fish enjoy (but don't require algae) I've got to add enough so that the other fish don't eat all the nocturnal fish food to satisfy all of them - in addition to their regular food. Or wait until night to feed the nocturnals - but some of my so-called nocturnals will wake up at feeding time and they'll fill up on flakes if they don't get their algae- so much for being nocturnal. Also if fish have small stomachs you could have fooled me, especially in the larger species, I have seen a DoJo consume a huge amount of flakes and then no less than 20 pellets AND an algae wafer all in one feeding. So I have no idea how much to feed any more and leftover food really messes up the Aquaclear to the point where they require weekly cleaning, sometimes twice weekly. They'll develop this thick brown grey slime all over the media and media basket until all the holes are clogged up. I noticed once I had to start feeding algae pellets or frozen algae along with bottom feeder pellets that also take time to consume I had to start cleaning the filter weekly - sometimes twice a week. Also remember to clean the media in a bucket of tank water NOT regular water or risk losing your good bacteria. Oh - and this is fun. There is a little spikey part that comes with each filter and there is no where in the instructions that I've found where it clearly says what it is or what it does. If this is driving you nuts - look on the bottom of the filter for a small hole and stick the little spikey part in that hole (some constantly fall out every time you remove the filter but over time they seem to cement themselves in the hole. This is Aquaclear's way of adjusting the TILT of the filter - if you want it straight or tilted more forward. In some situations it is critical part but I can't tell you the countless times I've been on my hands and knees trying to find one of these when it falls out. It is engineered stupidly to tilt the filter with this little plastic piece and then not clearly explain in the instructions what it's for. Oh - replacement parts are rather expensive $20-$40 for an impeller (for a $60 filter). Luckily I've never damaged an impeller. WARNING the holes in the intake tubes for the Aquaclear are rather large and break easy. That means the chance of a fish getting sucked up into the filter are very high. I recently lost 3 rather expensive young Glass Fish as well as a juvenile Yellow Pleco. Not only was this an expensive loss it was heartbreaking. I had been trying to get a hold of some glass fish for years but they were either not stocked or always sold out. Waiting lists didn't help - but the size that were sent to me were only slightly bigger than a fry and I forgot to do some maintenance of my intake tube. The worst was the pleco that actually ended up in the impeller - a horrible mess to clean up. The glass fish just sat on the sponge and died for reasons unknown - they looked perfect.
The good news:
That said, the Aquaclear is the only HOB filter I've found where you have space for a lot of different media. It is one serious filter. You can add sponge, charcoal filter and biobeads like it comes with, but there are times you may need to add other types of media to address certain problems in the tank and it readily allows you to add a variety of media making it the most flexible HOB on the market. (just remember to remove charcoal filters if you are dosing the tank with medication, or the carbon will absorb all medication - that is true for any filter). It is by far the most flexible HOB filter on the market (and the most expensive). If you want perfectly sized media you are stuck with purchasing their media at their prices, but I've found sheets of thick sponge that work far cheaper. As far as adding some additional sponge type media - you can buy bags of this thin finely wove sponge in the hobby section anywhere and add it as additional filtration and you can just toss it out and replace every week or two. In fact for saltwater tanks they actually make this type of filtration to remove excess phosphates from the water. It's funny to read their instructions for changing the media: every month change out the charcoal, every two months change out the sponge and every three months change out the beads - but don't change more than 1 or 2 components each month. Besides this being an impossible and expensive schedule to follow - your tank will be better off if you never or rarely change out the sponge or the biobeads - this is where a lot of your "good" bacteria live, Simply rinse them in tank water each month to get any goo off off them. I do change my sponge every few months because it starts to fall apart or smell badly but I have NEVER needed to change out the biobeads - I don't know if they are assuming that there is enough bacteria in the substrate that you can remove the biobeads every three months or what they are thinking. But don't follow those instructions, As far as c;leaning the Aquaclear You do get sort of used to cleaning these frequently but I wish they included a set of brushes for reaching into small places where mold or algae hide. (I'm looking for some small brushes with fringe on TOP not just on the the sides). If I'm going to go to this much trouble to clean these once or twice a week I want them to sparkle and shine (just remember never use any detergent product - just plain water to clean the housing. Clean the media in tank water but the charcoal filter can be rinsed in regular water or just tossed and replaced (rinse the new one first due to black dust). Some people think charcoal filters are useless but I think they are another important part of the system. Just like that's primarily what the Brita water pitcher uses. It does make my water taste better - perhaps the water tastes better for the fish if you use a charcoal filter.
As my tanks get bigger I'm converting all of them to cannister filters. I haven't reached a conclusion if that's better but they don't seem to get very dirty (just the media). I haven't quite got the method down for cleaning and changing out filter so keep a towel handy - they hold a lot of water. I expect the rules for media are the same as for the HOB's but there is so much more room for filter media I hope my aquariums that use a cannister all stay clean and bright for at least 1-2 weeks. They are noiseless. But for a 5-20 gallon tank they make no sense to use so there will always be a need for HOB's.
