DIY Filter

It seems the guy on monsterfishkeepers mistook cubic foot for gallons. The surface area of Pot Scrubbies is 370 per cubic foot, not per gallon. That comes out to 49.6 per gallon. However, he apparently did the same with bioballs so the ratio should be the same.

Ok, it seems Pot Scrubbies do outperform standard bioballs. However, cannister media made from porous ceramics can have a surface area of 150,000 sq. ft. per cu. ft. That is about 20,000 sq. ft. of surface area per gallon. Filling a few gallons would burn loads of money though. CerMedia runs about $245 per gallon. That is $661.50 to fill up the U-Sump I just put together. Having a small canister of it on the return side of the Pot Scrubbies would still be nice, but for any cheaper alternative the Pot Scrubbies take the win.

The surface area of the ceramic media may not all be effective surface area. Very small pores may exclude bacteria, or if they are just large enough for a few cells, quickly become clogged with dead cells and debris. A blockage affects surface area interior to it as well as the immediate blocked area by reducing gas and nutrient exchange. So, the effective surface are is likely to be considerably smaller than the advertised figure, helping to close the gap. If the ceramic media were as superior as claimed, you could filter quite a bioload with a single nugget of media.

The surface area of the ceramic media may not all be effective surface area. Very small pores may exclude bacteria, or if they are just large enough for a few cells, quickly become clogged with dead cells and debris. A blockage affects surface area interior to it as well as the immediate blocked area by reducing gas and nutrient exchange. So, the effective surface are is likely to be considerably smaller than the advertised figure, helping to close the gap. If the ceramic media were as superior as claimed, you could filter quite a bioload with a single nugget of media.

There is also the issue of oxygen supply. A single nugget is not going to have access to enough oxygen to break down as much ammonia as advertised. Nearby oxygen is not good enough and it takes two parts oxygen for every part ammonia it breaks down. There is also the issue of competition from other bacteria, which also use oxygen but does not break down the ammonia as such. Rather it simply breaks down larger organic compounds to smaller ones, like the dead cells you mentioned. These bacteria, unlike nitrosomonas and nitrobacters, can grow exponentially. So in 24 hours they can multiply more than the nitrifying bacteria can in a month if the food supply is there. Temp and PH also play a role in the rate nitrification can take place with a given colony of nitrifying bacteria.

The surface area at best provides a limiting potential. Actual results vary with too many variables to completely control, but all filter media choices have the same issues to one degree or the other. For ceramic pellets the issues you spoke of is primarily controlled by a very fine prefilter of the water before it passes over the media and other bacteria to remove the dead cells. The prefilter needs to be fine enough to filter microscopic algae.

So yes, you have a point, but when the differential in surface area is big enough and you control for some of the main issues then you can expect to get back a reasonable portion of that advertised difference. Especially since the media it is competing against has some of the same issues to one degree or the other. The fluidized beds Erica mentioned have an advantage that many of those issues are moot by design, with bubblers remedying the main issues not handled by the fluidized bed itself, but there is still the issue of competing bacteria. Especially with lots of larger organic compounds in the tank. Very fine prefilters help a lot with fluidized beds also. Pot scrubbers are a lot less efficient from the start but suffer less from at least some of the variables effecting its efficiency without trying to control them very much.

I think (hope) my upcoming HOB plant filter will be outdo them all in efficiency, ease of use, numbers of contaminant types it can filter (including metals), and the completeness of the filtering process. Nitrifying bacteria only do part of the contaminate breakdown, requiring you to do water changes to remove the unfinished components of the breakdown process. This is a limit of all bacteria based filters.

This is a limit of all bacteria based filters.

True. And that's a limitation that nitrogen removal by plant uptake doesn't have.

I think live plants in the tank are the way to go. They preferentially use ammonia over nitrate, so if there's an ammonia spike they take care of it. Honestly, I don't know why I still have filters on my tank anymore, since it's obvious the plants are the ones removing all the nitrate. (Here is a photo of my tank. You see why? http://gallery.nanfa...l size.jpg.html ) With this many plants it doesn't really matter what the nitrogen load is in the tank, they eat it all up. The water is constantly at 0 ppm ammonia, 0 ppm nitrite, and 0-10 ppm nitrate.

The only problem is when the plants aren't growing. If you don't have good lighting, the plants might be dying. That means that they're not only not removing the nitrogen, they're also releasing some as they die. That's why I have 2750 lumen, 6500 K bulbs Home Depot, $8 for two bulbs, $20 for the lighting unit. Very handy.

Edited by EricaWieser, 21 April 2011 - 10:03 PM.

I am sold on FB - have used it for years and it just plain works. LOW maintenance as well. And hey - it's cheap!

Newt's right about the ceramic media. That huge "surface area" claim may be technically correct for new clean media, but it's functionally meaningless. As soon as the media is colonized with biofilm, the usefulness of those tiny pores for nitrification is drastically reduced. (Yes they might provide a little anaerobic denitrification, but I'd be surprised if it's significant to water quality).

For a 3" pipe filter I would use small lava rock or coarse bone charcoal (Jungle Aquar Prod used to sell it; dunno if its still around). Pot scrubbers might be hard to get out if you cant get your hand inside, unless you string them like beads.

Erica -- Yes plant-based ammonia-removal is ideal for hobbyist tanks with small fish and lotsa growing plants like yours and mine. But for big messy fish or aquaculture situations where you're trying to grow a lot of fish in limited space, it may be impractical to rely solely on phyto-treatment.

Yes, I just checked and pot scrubbers are a bit snug in 3" inch pipe. If using them stringing them on high test line is advisable as you say. Either that or cut them in two. I will check the numbers on lava rock and bone charcoal and see what it looks like. The technical details I see are using units that require a few more conversions than normal for a direct comparison, so I will get to it shortly.

What you said about plant-based ammonia-removal is the reason the HOB design I will be putting together soon is somewhat more akin to hydroponics. Though some soil substrate may be used plants will not depend on the CO2 content of the aquarium water, as they are exposed to air with root providing oxygen in the substrate for symbiotic bacterial growth and using the CO2 and other products from that. Hence it will not require space in the aquarium so there is nothing that destructive fish can get at. Plant roots have evolved to maximize and symbiotically work with nitrifying bacteria, thus likely outperforming any bacterial media we have come up with. It also provides a refuge for colonies of live food which overflows continuously with the water flow. For larger aquaculture situations the HOB can be replaced with a sump setup where the sump grows plants rather than just bacteria. Perhaps using a large $10 childs swimming pool, or larger constructs for commercial situations. The key is modularity with separate habitats working together.

I was messing with one of the pot scrubbers and noticed that it would unroll into a long sock like structure. Hung loosely it was a full 3' feet long, easily stretched over 5' feet. This means that I can unroll the scrubbers and connect them together in series to make a single length that goes all the way through the filter. Then connect a bunch of those in parallel to make it thick enough to fit the pipe however snuggly I want. The whole thing would be tied as a single piece making removal trivial.

Well that makes it easy: Just unroll and stretch out the pot scrubbers, bundle them together like sticks until you've got the right diameter, and stuff the whole bunch inside another unrolled pot scrubber. I'd use two separate bundles: one for the downflow pipe, one for the upflow pipe. One continuous bundle through both pipes may snag in the bottom U. Also, two pieces lets you clean them at different times. Could also do this with plastic mesh onion/grapefruit bags.

Now, i just wonder what sorts of plasticizers, EDCs, other synthetic organic crap might slowly leach from pot scrubbers? Oh well, i guess that's why we change water.

Edited by gerald, 25 April 2011 - 01:21 PM.

I like your idea of pairing them inside a pair of scrubber socks. That does away with weaving them together with fishing line or something similar and, as you say, allows replacements without killing the whole active media. The bottom part of the U can still be used by adding a more traditional bio-media.

In the long run this will likely be kept active by use on plastic totes, such a tadpoles which can be messy. But with my planned experiments I need a large backup filtration system for the tanks in the event the experiments do not go well. I also need good clean holding totes for the fish in case they have to be removed from the tanks for any length of time. The experimental nature of upcoming designs requires me to be prepared for failure.