First Impressions and Breakdown: Penn-Plax Cascade 300 Internal Filter

Like many beginning fishkeepers, I got into the hobby with a basic kit that included a tank, heater, and HOB filter.  I liked the function of the HOB well enough that I didn’t really investigate other forms of filtration; the next time I needed a new filter, I went out and bought an AquaClear HOB.

Now, don’t get me wrong:  I have no complaints about the AC filters or any of my other HOBs.  But I’ve been thinking lately about exploring other filtration options, partly because my fishroom setup limits the amount of space I have for HOBs.

This week, I stopped by a chain pet store and picked up the Penn-Plax Cascade 300 internal filter.  It’s rated for 70gph and is marketed as appropriate for up to a 10-gallon tank.  The filter breaks down into several components (see photo gallery for detail):

Cascade 300

Cascade 300

  • the impeller/motor unit
  • 2-piece media chamber
  • air intake with muffler
  • output flow nozzle
  • 90° tube
  • spray bar
  • airtube clip
  • impeller cover
  • impeller

Also included are a carbon cartridge and a mechanical/biological filter sponge.

As of this writing, I haven’t set the filter up in a working tank (meaning I can’t speak to its long-term effectiveness or durability), but I like the design.  UPDATE:  After setting the filter up, I still like it! I’m currently running two of these on different tanks.


  • Refillable carbon cartridge allows you to refill with any brand of carbon or other filter media
  • Removable carbon cartridge allows that section of the media chamber to be used for other media
  • Optional spraybar is included.
  • Optional air intake is included and has a clip to hold it in position.
  • Reasonably compact design (obviously it takes up more room than a HOB intake).
  • Clear media chamber allows easy viewing.
  • Filter is easy to modify.
  • Intake design allows for maximum surface area on sponge to be exposed to water.
  • All outputs swivel for directional control.
  • Flow rate is adjustable.
  • If it lives up to its rated 70gph, it circulates the water faster than many “up to 10 gallon” filters on the market.


  • Internal filters in general will have the inherent con that they must be removed from the tank to be serviced (unlike HOBs or canisters, which usually only need to be turned off for service).
  • Air intake can only be used with the flow nozzle, not the 90° tube attachment.  This isn’t a big deal when you’re using the spraybar, but it might limit modification options a bit.
  • Flow nozzle output is semicircular in shape rather than circular, making it difficult to modify by adding extenders of any kind.
  • Odd design decision on the intake end of the media chamber might allow water to bypass sponge (see photographs and comments below).
  • Ideally, on a 10-gallon tank, I’d want 100gph.

Potential issues

The tube running up through the center of the sponge compartment is slotted on the sides, allowing water to enter the sponge through its central opening, but it also is open on the end.  It seems to me that this allows a lot of water to completely bypass the sponge.  Not counting whatever bacteria grows on the carbon pellets, the sponge is going to house the greatest amount of bacteria, so this is a problem.

Potential modifications

Other than filling the media chamber with media of your choice, there are other options for modifying this filter.

The 90° tube on the output should accommodate third-party or DIY attachments.  A flexible hose could be fitted snugly over the tube and used to connect to any number of fixtures.  Unfortunately, the flow nozzle would be harder to fit to custom attachments due to its shape, and this is the only output attachment that includes an air intake.

I think before I put this filter to use, I’m going to cap or plug the end of the tube running up the center of the sponge compartment.

Removing that center tube using a Dremel or similar tool would allow third-party sponges or other filter media to be stuffed into the chamber fairly easily at the cost of some sponge surface area.  If you’re going that route, you could drill or cut extra holes into the chamber wall to allow more sponge to be exposed.

Final verdict

In general, I like the filter.  In my opinion, it needs a little aftermarket modding before it will reach its full potential, but the modifications I have in mind are simple enough to do.  Assuming the filter is reliable and effective, I’ll probably buy another one like it at some point in the future.

I don’t make a habit of using carbon in my tanks, so I’ll probably replace the carbon cartridge with some form of biomedia (ceramic media or lava rock, most likely).


The “final verdict” hasn’t changed, now that I’m actually using the filter. 🙂 Check out my post on how well the filter performs.

Disclaimer: This is an unsolicited, unsponsored review. The seller or product manufacturer has not reimbursed me in any way for this review. My opinions are my own; your mileage may vary.