top of page

The Fishroom Diaries-Back to the Lowly Box Filter

Have you ever noticed how for some people, the aquarium hobby is as much about filtration as it is about the fish? I can remember my first aquarium- a five gallon metal framed tank with a small corner box filter. The filter media were “angel hair”, or spun glass, and charcoal. At that time, I had no concept of biological filtration, and the entire filter contents was discarded and replaced monthly, which meant that water quality probably worsened every time I “cleaned” the filter. From there, I migrated to undergravel filtration, hang-on-back power filters, canister filters, wet/dry filters, and sponge filters. For a long time, I relied on various size Aquaclear power filters for most of my tanks. These filters were fairly reliable, but at some point, I ran out of electrical outlets.  I was also tired of having the filters stall-out and not restart after intermittent power failures. When the impellers got stuck, the units would produce heat and generate a noxious anaerobic soup in the filter box; this meant that the filter had to be removed and thoroughly cleaned before restarting. Other problems were caused by snails clogging up the mechanics, or heavy mats of algae growing on the sponges and inside the intake tubes.

Finally, I broke down and purchased a decent sized air pump and a distribution manifold so that I could run several air-driven filters from a single electrical outlet. I tried both homemade sponge filters using Poret foam, and the commercial Hydro sponge filters. While both provided adequate biological filtration, they did not trap larger debris as well as the HOB filters, so I was having to bottom siphon more often. I was thinking of ways to enclose the sponge filter in some sort of plastic container that would also serve as a settling chamber for trapping debris, and it finally dawned on me that I was basically just reinventing the old box filter.  I searched online for some economical box filters, and found that there aren’t many options out there. Most vendors only offer two brands, Lee’s and Pennplax. You would think that with so much of the market cornered, these models would be engineering marvels…but not necessarily so; you would be surprised at how lacking some these units are.

Pennplax “jumbo” 5 1/2″ box filter

I first tried the less expensive Lee’s Tripleflow filters; while the basic design is good, the quality of the manufacturing is very poor. The plastic is very thin and brittle, and there is no stem for attaching the airline. Instead, the airline is supposed to be held in place with three tiny plastic prongs that will break off with the slightest pressure. The “discard a stone” type air stone is too light weight and will float to the surface since the broken prongs can no long do their job, and the unit is rendered useless. Next, I purchased two sizes of the Pennplax box filters: a 3” square filter, and a 5 ½” round filter. The smaller square filter looks nice, but I found that in most cases, the air rose up through the filter medium rather than through the center riser tube. In order to create enough resistance to prevent this, you must pack the box with a fine charcoal, but this made cleaning very difficult.

The ultimate winner was the Jumbo Pennplax round box filter.

Without going into too much detail, I tried a variety of filter mediums in search of a cheap, readily available option, and I eventually settled on crushed lava rock, and plastic pot scrubbers from the dollar store.  The crushed lava rock can be purchased at Home Depot in the plant section; it is used as a decorative soil cover for potted plants. I have previously used pea gravel in my filters, and I can say that the porous lava rock is much better at providing biological filtration. The pot scrubbers are round, and can be separated from the middle to fit around the filter’s lift tube. These materials provide lots of surface area for nitrifying bacteria, and they do a fair job of trapping debris without clogging up too quickly. For the clearest water, some filter floss could be loosely packed in top of the filter, but this might necessitate more frequent cleaning. I am now a permanent convert to the good old box filters. They are scalable, inexpensive, uncomplicated, and they won’t run up your electric bill either.

16 views0 comments

Recent Posts

See All


bottom of page