7.2.8. Pot Scrubbers

Pot scrubbers have the best combination of biofiltration capability, ease of use and availability of any biomedia. Extensive testing has shown it to be a very good media to put in an aquarium filter.  If one is a nerd like the author one might be interested in this long boring article on why this is true. It includes testing which proves this is true.

Pot Scrubbers in Depth

Pot scrubbers go by several names, including mesh scrubbers, pot scrubbies, plastic scourers and scouring pads (one actual description was “plastic pot round scrubber scouring pad plastic” LOL). And there are several other varieties of pot scrubbers given the same names. This makes shopping for this media a bit of a challenge. Amazon has them listed under “Assorted color round nylon fish scouring pads“ (24 pot scrubbers for $8).

I recommend buying pot scrubbers at the local Dollar Store (if you can find them). A comment to this website on Amazon pot scrubbers is pertinent:

“Sadly, Pot scrubber from amazon quality is down the hill recently. Not only it become way smaller (compare to 3 years ago), it also have bigger holes and less density. It is less weaved and it break down in a week even using for cleaning dishes. the plastic break so easily. It is cheaper but quality got worse. If buying from amazon read recent reviews, you can see it is poorly made now”

A surface area for pot scrubbers calculated was based on simple math calculations by a reader.

“I did a little checking, tore apart a pot scrubber measured the width of the strand at 1mm wide. Placed the unrolled scrubber over a 3″ pvc and pulled 8 meters of strand from 10 rows of stitching. Counted 140 to 150 rows of stitching on a couple of scrubbers. So 800 mm per row of stitching with 2 sides of the material that’s 1600 mm sq area per row x145 rows average. That’s 232,000 sq mm area per scrubber, convert that to sq ft 2.49 square ft per scrubber.. round out a bit that’s 50 pot scrubbers per pound of fish metabolic weight with a bit of wiggle room. I picked up 7 packs of 7 scrubbers at the dollar store for under 10 bucks. Cheapest filter media ever made. Also, the material is 100% nylon.”

Types of Pot Scrubbers

There are several types of “pot scrubbers”:

1, There are the non-woven rectangular pads of thin plastic fibers about 5 thousands-of-an-inch in diameter. These are typically dingy green in color. These can be used to replace cartridges in cartridge type mechanical filters but they are not useful as a biofilter media.

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2, Then there is a softer “natural” sponge on it, with holes that are of many sizes and shapes, generally bonded to one of the pads above. This is a cellulose product which will disintegrate in weeks in an aquarium. Avoid them.

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3,  Then there are urethane foam and melamine foam (“Magic Eraser”) pot scrubbers. These have too small of a pore size and do not work well as filter media.

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4, Then there is the “plastic pot scrubber”. These are like a doughnut shaped ball of thick plastic fibers about 30 thousands-of-an-inch in diameter. These are brightly colored in lots of shades. This is useful for filtration and is what we are talking about in this article.

The latest price as of December 2021 is 24 pot scrubbers for $8 on Amazon listed under “Assorted color round nylon fish scouring pads “. But note with COVID the price and availability are fluctuating wildly.

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Calculating the Number of Pot Scrubbers Needed

A question and answer from the comments section of this website will be instructive here:

Question:

“I would like to get the Eheim 2260, which has 18 liters room for media. After reading your filter media comparison test articles, I intend to fill this thing up with pot scrubbers, as the price/performance ratio is unbeatable.

I have no idea on how many average sized scrubbies would fit in such a volume (tightly packed too). You have a lot of experience with this kind of media, could you please provide me with an estimation?”

Answer:

“OK 30 small (2.5 inch by 1 inch) pot scrubbers are now for sale on Amazon at $18. There is roughly 8.7 small pot scrubbers per liter. Or you will need about 150 (8.7 x 18) small pot scrubbers, 5 packages or $90 worth of small pot scrubbers.”

This is the result:

Pretty darn good calculations! 150 calculated versus 154 actual!

The data which gave this number is as follows

30 small pot scrubbers from Amazon (2.5 inches in diameter, 1 inch thick. 4.9 cubic inches) filled a box with the dimensions 3.5 inch by 5.5 inch by 11 inches. This is 212 cubic inches, or seven cubic inches per pot scrubber. This means 30% of the box is free space between the scrubbers. This works out to be $0.086 per cubic inch or $0.60 per pot scrubber.

• one liter is 9 pot scrubbers at $5.24
• one gallon is 33 pot scrubbers at $19.87
• one cubic foot is 247 pot scrubbers at $148.20

But there has to be a caution here. Some of these pot scrubbers are four inches in diameter and one inch in thickness. And some of plastic pot scrubbers (like the ones from Amazon above) are about two and a half inches in diameter and an inch in thickness. The four inch pot scrubbers have a volume 2.5 times that of the small pot scrubbers. If you buy the four inch ones the numbers above need to be changed to

• one liter is 4 pot scrubbers
• one gallon is 13 pot scrubbers
• one cubic foot is 95 pot scrubbers

This is a BIG difference! Also note that the price also varies a huge amount by country. In some countries plastic pot scrubbers are very cheap and in others very expensive.

Comparative Costs

There is a problem with plastic pot scrubbers as far as cost in the USA. I cannot find a bulk supplier that will sell more than 30 pots scrubbers at a time for roughly $20 for one gallon. There thus is no huge savings to be had by buying in bulk. If you have a large filter this can be a problem.

The K1 media, which has very close to the same performance, is $25 if you buy one gallon, $55 if you buy one cubic foot (that is $7.33 per gallon). On eBay you can buy 2 cubic feet of K1 media for $70. That is $4.67 per gallon or $1.24 per liter when you buy K1 in bulk of two cubic feet.

So if one has a single small canister with only one gallon of capacity, buying the pot scrubbers makes sense. But remember, this hobby is addictive. Invariably you will be getting larger and larger tanks and more and more filters. So buying two cubic feet of K1 type media and filling the small canister with that, also makes a lot of sense.

Testing Pot Scrubbers

In a test of ammonia oxidizing capacity of various filter media under actual aquarium condition plastic pot scrubbers performed extremely well. They outperformed K1 media and were some five times better than lava rock or ceramic rings. So this is an excellent media for all submerged media filters. This was quite surprising as the surface calculations for pot scrubbers said they were not all that good.

A test of ammonia oxidizing capability of various filter media was run. The first number, the “efficiency” is the average ammonia oxidizing that 15 cubic inches of media accomplished over a 90-day period. The second number is the “effective” surface area in square feet per cubic feet calculated from that test. The third number is the effective surface area in square feet per cubic feet calculated by simple mathematics. The correlation between the test results and the calculated surface area is very significant and means the testing was accurate.

The higher the numbers here the better the media. The plastic pot scrubbers did surprisingly well in the test. In all probability this was due to their porosity. Pot scrubbers have a very porous structure which allows the rapid flow of water through them. This porosity also allows brown gunk to build up in the spaces. Brown gunk has a very large effective surface area. Plastic pot scrubbers are an excellent media for canisters and sumps.

Static K1 media is probably equal to the pot scrubbers in function but it is only inexpensive in bulk quantities of cubic feet. Since 30 ppi foam can be expensive (Poret isn’t cheap), has to be very carefully cut to minimize flow around and because 30 ppi foam will plug up in some situations, pot scrubbers are probably the best all around media out there for small filters. In larger filters the K1 begins to have a decided cost advantage because it is cheaper in bulk.

A pot scrubber gives equal filtration in both a large and a small filter. One might have to cut up the pot scrubbers for a small filter but that does not change their efficiency. The open volume is about 80%. Now if the flow is low then pot scrubbers will fill with brown gunk. And brown gunk has surface area, which is good. If the flow is fast, little brown gunk will form but the biofilm which is there is more efficient. So you have two competing things going on. So predicting the performance in any given situation is not exactly an exact science.

KaveMan Aquatics

Kev at Kaveman Aquatics YouTube channel recently did a video where he replaced all the ceramic media in the baskets in his canister filter with pot scrubbers for three months. After three months the water to his heavily stocked aquarium had changed from “dull” to “crystal clear”. Others have sent comments to this website where they replaced all their expensive “stuff” with pot scrubbers and got excellent results. It is all anecdotal and I generally avoid anecdotal but someone might be interested.

An Important Caveat

There  is one problem with pot scrubbers. They are made of polyethylene plastic and are very open in their structure. Polyethylene is very lubricous and few things stick to it. So if one holds a pot scrubber under running water or vigorously swishes it back and forth in a bucket, virtually all the beneficial bacteria will be swept out of the structure.

In all but very heavily stocked tanks pot scrubbers should never need to be cleaned. If they become so plugged up that flow is obviously around them and not through them one can lightly clean then in a bucket with a few squeezes’ to each pad.

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