Sump with only sponge?

[David R]

Drawing up plants for a sump for my next tank and I'm trying to come up with a sump that is both low maintenance and quiet. I'm toying with the idea of using K1 fluidised with a powerhead (to keep the noise down) and Poret foam for the mechanical filtration. But then I though in the interests of simplicity why not just have a big fat stack of sponges like a giant thick HMF filter that does both mechanical and biological, with he first couple of sheets being cleaned more frequently and the ones further along less often. Here's the sump on my old 2000L tank, the Poret worked really well in this way, though after the video I put a sheet of egg crate behind it to keep it flatter, the first two sheets needed rinsing every 2-3 weeks, I'd do the other two every 4-6 weeks but they probably could have lasted six months. The one problem with doing it vertically is that it requires more space above to remove for cleaning, so in the new sump I'll probably have to do it horizontally. Obviously the K1 has a higher surface area for the same volume, but either way I don't think I'll have trouble fitting in enough media for the amount of fish. The K1 also has the advantage of never needing to be cleaned, but on the other hand aside from the first couple of sheets (which I'll need to run with the K1 anyway) the lower sheets might only need to be rinsed every 6-12 months. The downside of the K1 is that it requires additional equipment, which will costs more up front and also in ongoing running costs and will also create more noise.

It almost seems too simple, why don't more people use sponge for biological filtration in sumps over stuff like ceramic rings?

 

[jjohnwm]

If you do a search online, you will likely find a few sources that disagree about the actual surface area per unit volume of various biomedia...but virtually all of the comparisons show that foam like Poret and others compares very favourably with media like Bioballs and K1 in terms of surface area. IMHO the big difference is, as you stated, the need for and ease of cleaning.

Ceramic media are very poor in terms of surface area compared to the other two. They work because the surface area required for a sufficient bacterial population is far less than most people believe. People use canister filters that have relatively tiny chambers for the biomedia, and yet have no problem. Then the same folk upgrade to a sump, and for some reason believe that they now need vast chambers chock full of biomedia to work properly.

My standard DIY sump design has worked beautifully for me for at least 15 years. It uses Poret foam slabs for mechanical filtration, usually with 3 layered pieces. The first is removed and rinsed frequently, often every day when I am home but it can go for at least a couple weeks without if necessary. The 2nd and 3rd layers are rinsed less frequently, and can go for long periods without clogging. I like the ease of frequent rinsing as it removes large amounts of solid waste before it has a chance to be broken down by bacteria, thus reducing the rate of nitrate accumulation in the tank.

The foam works great as a biomedium as well as for mechanical filtration. Hamburg Mattenfilters are fantastic for smaller tanks, and they use one piece of foam for all their mechanical and biological filtration. But they are a bit of a pain to clean, and they don't remove anything from the tank system so all waste is broken down and contributes to nitrate buildup.

Why don't more people use foam for all their mech and bio needs? I think a lot of folks are as interested in gadgets and gizmos and tech as they are in the fish. They post pictures of the insides and under-tank areas of their aquarium stands, ooohing and aaahing about nice clean installations and expensive boutique filtration media as though that were the main goal of fish-keeping. Maybe, for some folks, it is. Foam slabs aren't cool and sexy; they don't look high-tech...'cuz they're not!...but they work very well, are very simple, are among the cheaper options in terms of media, are pretty much permanent (I have Poret sponge filters and slabs that have been in continuous use for a couple decades and are still perfectly fine)...they're in many ways the perfect filtration media. But...they ain't cool.

But that's what the fish are for!

 

[duanes]

Many aquarists believe the more biomedia you stuff into a sump, the better.
The reality is, its the food to micro that-organism ratio that determines efficacy in filtration, not the amount of media.
In my 125 sump I use a wall of porrett foam for mechical filtration, and three 5¨(13 cms) bags of biomedia.
above my ammonia test, below nitrite.

The fish load in the main 180 gal tank averages 20 medium cichlids.
Below the mechanical, and biomedia.

The rest of the sump, is heavily planted

This not only helps with ammonia and nitrite
But also removes nitrate

The nitrate test above, was done yesterday, but is average , and the tank has been set up this way, for over 5 years.
I rinse out the porrett foam about once per week, amd do water changes, that´s about it for maintanance other than cleaning detritus from screens.

I also think of the planted sump as aesthetically pleasing as the main tank.
Beside the plants, I keep a cadre of shrimp to help police up extra detritus. on the porrett, and because the sump sits in full sun,
there are a few juvie placos to help keep algae growth on the glass.

I don´t think of a sump as only a utilitarian box for stuff, but as its own biological , and beautilul adjunct.

 

[David R]

Great responses, thank you!

jjohnwm I'd be interested to see a picture of your standard sump design. What do you use for bio media after the foam? I totally agree about people wanting stuff that "looks cool" when it comes to filtration, I've seen some crazy set-ups with multiple chambers fill of every imaginable type of bio media, as though they someone magically perform different functions. There's nothing glamorous about a sump that's just a giant sponge filter, but if it works it works. KISS is good when it comes to filters IMO.

duanes I get what you're saying about the amount of bio media required, and it's interesting to see just how little it is possible to get away with in contrast to the usual "more is better" approach. And I love your planted sump! I was thinking of having a chamber before the mechanical filtration to grow Pothos in as some of the fish in the main tank will likely nibble the roots. AFAIK terrestrial plants are far more effective at removing nitrate, but having a planted tank section like that is certainly more appealing to the eye. We don't get FW shrimp here in NZ unfortunately, but there's plenty of small interesting fish that would be fun to keep in a planted sump like that. Do you think it has a noticeable impact on the nitrate levels? Glad to see there's still a few names I recognise around here, I haven't checked in for years!

 

[duanes]

The Paratya fresh water glass shrimp is native to New Zealand.
It begins with a marine stage, then moves into fresh water.

You also have a native mangrove tree that may be interesting to try in a sump, it is said to grow somewhat smaller, so may be more manageable.

I have been picking up, growing Panamanian mangroves in my sump, I first started finding the pods floating in the Pacific near the beach, and found they are able to grow salt, brackish and fresh water.
They started simply, as below in a sand filled bamboo stem

and over the last couple years grown the classic aerial roots.


The emergent foliage section has grown 6 ft above the sumps water surface.

Before I got hooked on mangroves, I was using Papayrus in the sump to suck up nitrates.

I hear there is a variety, that grows endemically there in in kiwi land.

And yes, any of these aquatic, semi aquatic, or even terrestrial plants with roots draped in the water, make a noticeable impact on nitrate reduction,
I have had numerous periods where our water plant was shut down, and it was impossible to perform water changes for weeks on end over the last 5 years, and with the planted sump, nitrate never exceeded 5 ppm.

 

[jjohnwm]

jjohnwm I'd be interested to see a picture of your standard sump design. What do you use for bio media after the foam? I totally agree about people wanting stuff that "looks cool" when it comes to filtration, I've seen some crazy set-ups with multiple chambers fill of every imaginable type of bio media, as though they someone magically perform different functions. There's nothing glamorous about a sump that's just a giant sponge filter, but if it works it works. KISS is good when it comes to filters IMO.

It's tough to get a pic of my setup; I'll see what I can do. Sadly, even if I manage to get an overall view of it, there's not much to see. It's essentially an opaque Rubbermaid Roughneck garbage can standing next to the aquarium (which in this case is a plywood box with an unfinished exterior). Water overflows into the top of the garbage can, down through three layers of Poret foam stacked horizontally in a pail, and then down through roughly 30 gallons of my top-secret super-biomedia: plastic shotshell wads that are sold for reloading shotgun ammo.

These things look like magnum-sized K1 cylinders to a casual observer, but they are completely invisible in this application within the garbage can, where they function as a "wet-dry trickle-filter" as we used to call it. The water drains out through a bulkhead at the bottom of the garbage can and into a bin under the aquarium, from which it is pumped back into the aquarium. The bin is where any heaters, if used, are located. It's also where I like to keep a DIY Poret sponge filter or two bubbling away, ready to be removed and used elsewhere to create an instantly-cycled tank for quarantine, hospital or other purposes.

Finally, the bin or bins under the tank are easily able to handle the flowdown from the aquarium, without overflowing, if the pump fails or is turned off for some reason. It's amazing how many of the expensive commercial sumps on the market utilize some tiny little pump compartment, usually at the tail end of a ridiculous string of unnecessary partitions. The pump compartment is the only place in the system where water levels drop due to evaporation or removal. Life is much better when that compartment is plenty big.

I used clear Rubbermaid-type bins for that bottom portion for years, but I found that they tended to get stiff and eventually start to crack and leak after a few years of use. The heavy-duty opaque ones seem much more durable, but don't allow visibility, so they aren't great if you want to use part of your lower sump area as a refugium for plants or animals. Up until recently I had a clear bin down there full of actual K1, spinning and gyrating like crazy. My granddaughters loved it; they've now pretty much outgrown the fascination, so I removed the K1 as I found it to generally be a PITA. The tank runs perfectly with no media at all in the bottom sump, as the trickle filter is still far more than required for the bioload even in three 360-gallon tanks hooked up in parallel with it, as I had in my previous house.

I was looking at the pics of your DIY sump; it's a work of art compared to mine!

 

[celebrist]

I am also an advocate for open, planted, and inhabited sumps. I use poret as a section divider and have bags of media, enough that I can grab one to seed a tank without effecting the main system

 

[thiswasgone]

Drawing up plants for a sump for my next tank and I'm trying to come up with a sump that is both low maintenance and quiet. I'm toying with the idea of using K1 fluidised with a powerhead (to keep the noise down) and Poret foam for the mechanical filtration. But then I though in the interests of simplicity why not just have a big fat stack of sponges like a giant thick HMF filter that does both mechanical and biological, with he first couple of sheets being cleaned more frequently and the ones further along less often. Here's the sump on my old 2000L tank, the Poret worked really well in this way, though after the video I put a sheet of egg crate behind it to keep it flatter, the first two sheets needed rinsing every 2-3 weeks, I'd do the other two every 4-6 weeks but they probably could have lasted six months. The one problem with doing it vertically is that it requires more space above to remove for cleaning, so in the new sump I'll probably have to do it horizontally. Obviously the K1 has a higher surface area for the same volume, but either way I don't think I'll have trouble fitting in enough media for the amount of fish. The K1 also has the advantage of never needing to be cleaned, but on the other hand aside from the first couple of sheets (which I'll need to run with the K1 anyway) the lower sheets might only need to be rinsed every 6-12 months. The downside of the K1 is that it requires additional equipment, which will costs more up front and also in ongoing running costs and will also create more noise.

It almost seems too simple, why don't more people use sponge for biological filtration in sumps over stuff like ceramic rings?

As duanes stated bio-filtration is a microorganism controlled biological process to perform the chemcial reaction ammonia oxidation (nitrification); more commonly known as the nitrogen cycle. Since microorganisms control each step of the nitrogen cycle to create a bio-filter we need to maximize surface area (their home) in a constrained area of concentrated flow (food delivery) to have the most efficient bio-filtration. More specifically, the bacteria species that do all the chemical conversions in the nitrogen cycle will attach themselves onto any available surface then develop a biofilm as the colony grows if there is sufficient food + oxygen (nitrification/nitrogen cycle is extremely oxygen reliant). Ergo, we can intentionally direct the growth of beneficial bacteria colonies within our aquarium through deliberate bio-media placement and "high flow" through that media. More importantly, since nitrification is the process of converting ammonia into nitrate the main source of the bacteria's food will be your fish feed. Your choice in what filter style to use should revolve around specifically your level of stocking and how much you feed.

Now why don't more people use sponge filters? Simple they clog more easily. Because the pores get clogged easily (and the internals typically remain partially gunked up depending on pore sizes) the effiectiveness of sponges are always decreasing as time goes on. We can prove this both by visually staring at a sponge only bio-filter over the course of several months or through math.


Of course the math option is extremely convoluted (the real calculations and explanations would be an academic paper on it's own) so I'm going to simplify things as much as possible without getting too technical. Specifically here are 3 baseline equations for people to follow along.

1) Rate Law (or rate equation): A type of mathematical expression that describes the relationship between the concentration of reactants and the speed of the associated chemical reaction.

• Just know that this is for a Chemical reaction but can be used to express other physial things. Not really too important to get into the weeds of what each variable represents. Since it is used to describe the rate of chemical processes, since we are working on the microlevel, I will be leveraging this base formula to create an equation to show the theoretical maximum amount of ammonia certain media can process.

2) Monod Equation or Monod kinetic: A mathematical model used to determine growth of microorganisms; a type of rate law

• μ: Specific growth rate representing the biomass produced per unit of time.
• μ_max (Maximum Specific Growth Rate): The maximum attainable growth rate of the microorganism.
• S (Substrate Concentration): The concentration of the limiting nutrient in the environment.
• K_s (Half-Velocity Constant): The substrate concentration at which the specific growth rate is half of the maximum (μ = μ_max/2)

3) Rv = A * K * (S / (Ks + S)): A bare-bones rate law/expression I made to describe the ideal Monod equation based on the media I will be comparing 20 PPI vs K1 Kaldness

• Rv (Volumetric Removal Rate): How much Ammonia removed per unit of reactor volume per day ( [g/(m^3)]d grams per cubic meter per day).
• A: Surface area of the media
• Other variables: plug-in from monod where "substrate" is ammonia

Granted there are a few jumps in steps/logic here but trust me in that the more detailed explanations would take too long to type out here in a single reply. In that same vein of thought, allow me to put some assumptions for the ideal conditions:

• K = 1 as we are working under the perfect Kideal
• S = Let's go with something slightly large but not insane like 5ppm of ammonia
• A_20PPI = 1,266 m^2/m^3 (swisstropicals poret foam claim based on https://www.swisstropicals.com/library/swisstropicals-poret-foam/)
• A_K1 = 800 m^2/m^3 (swisstropicals claim based on https://www.swisstropicals.com/library/swisstropicals-poret-foam/)

We get:
Rv_20PPI = 1,266 * 1 * ( 5/(.5+5)) = 1150.90909091 [g/(m^3)]d
Rv_K1= 800 * 1 * ( 5/(.5+5)) = 727.272727273 [g/(m^3)]d

At face value it would appear the foam is ~63.2% better than K1 Kaldness but this only describes an ideal situation where all surfaces get covered in nitrifying bacteria with 100% efficiency. If we modify the rate law to include one extra term, Effectiveness Factor (η), which describes how efficient all surfaces are between 0 and 1 (0 being the entire surface area is 0% active and 1 being 100 active.) we should see different numbers but the same ratio. The new equation would look like: Rv = A * K * (S / (Ks + S) * η

Rv_20PPI Rv_K1

100%: 1150.90909091 [g/(m^3)]d	100%: 727.272727273 [g/(m^3)]d
80%: 920.727272727 [g/(m^3)]d	80%: 581.818181818 [g/(m^3)]d
60%: 690.545454545 [g/(m^3)]d	60%: 436.363636364 [g/(m^3)]d
40%: 460.363636364 [g/(m^3)]d	40%: 290.909090909 [g/(m^3)]d
20%: 230.181818182 [g/(m^3)]d	20%: 145.454545455 [g/(m^3)]d

As expected the foam still keeps the ~63% lead but there is one last factor missing; the clogging of the pores. Let us add one final term to the equation: Rv = A * K * (S / (Ks + S) * η * f(clogged) again between 0-1.

η = f(clogged) for the table below
Rv_20PPI Rv_K1

80%: 736.581818182 [g/(m^3)]d	80%: 465.454545455 [g/(m^3)]d
60%: 414.327272727 [g/(m^3)]d	60%: 261.818181818 [g/(m^3)]d
40%: 184.145454545 [g/(m^3)]d	40%: 116.363636364 [g/(m^3)]d
20%: 46.0363636364 [g/(m^3)]d	20%: 29.0909090909 [g/(m^3)]d

And of course since we are only tacking on an addition multiplicative term the ratio remains the same with 20 PPI foam retaining a decisive ~63% lead! Except it is clear to anyone who has used foam for an aquarium application that it will get clogged and that the internal pores do not all get the same flow or nutrient ratios as the initial surfaces.

The realistic values for η and f(clogged) for Rv_20PPI should be between .5-.6 in a realistic use case while K1 would be closer to .8-90 giving us:

η = f(clogged) for the table below
Rv_20PPI Rv_K1

60%: 414.327272727 [g/(m^3)]d	90%: 589.090909091 [g/(m^3)]d
50%: 287.727272727 [g/(m^3)]d	80%: 465.454545455 [g/(m^3)]d

Resulting in K1 Kaldness being ~62-70% more efficient.

Of course if you can somehow keep your 20PPI sqeeky clean it is without a doubt better than K1 with this quick and dirty math but again there is so much more that goes into nitrification. Stuff like temperature, pH, flow rate, etc. all can influence how effective your bio-filter is. This isn't even going into how 20 PPI is typically not at 1,266 m^2/m^3 or the fact that you would need consistantly clean 1 cubic meter of the material to get these insane results. At the end of the day MBBR are typically more consistant at ensuring the maximum amount of ammonia removal with the least amount of effort on your part after setup + it scales much easier.

Regardless of what style you choose IMO the best bio-filter is one you will maintain and tolerate having to (inevitable) move around. Although MBBR mathematically check out in terms of efficiency and scaling double check what you actually are keeping and if you need something that beefy. If your stock + feeding schedule/amount doesn't really add that much waste into your system do you really need the most efficient nitrifying system? Can you stand hearing an air pump 24/7? There are a pleathora of other questions you need to ask yourself that only you can answer.

HTH