Is Undergravel Filter Good For All Corydoras?

[bunthid tumnontigoon]

Hello! Everyone

I have some questions about "Undergravel Filter". I have some Wild Corydoras that I really love them very much, and I am trying to keep them in an excellent condition for a long time, so I really want some information about them. I have heard that "Undergravel Filter" is an excellent for a small tank. Is that true? How about a big tank, is that an excellent for it? Can someone tell me the true? I set up my big tank ( 60 gallons custom tank ) with "Undergravel Filter", and have some Wild Corydoras in there. But, I am not sure about this. I should keep like this, or I should remove it.

I have heard "Undergravel Filter" has positive way and negative way when you set up your aquarium tank. Is that true? I have heard that there is lots of bacteria under the gravels if you keep for a little while, and you have to clean all up by remove everything from your tank because if you don't remove everything, you can not clean "Undergravel Filter". Is that true? But, the negative way is it will keep your tank clean for a small tank only. Can someone help?

I don't know should I still keep my "Undergravel Filter" for my Wild Corydoras or should I remove it, and set up with other filter. If that true as questions I have been asked, so "Undergravel Filter" is not good for a big tank because it will be so hard to remove and clean all materials in a big tank. Please! help. I don't really know and I am not sure about this. Thank you very much.

Bunthid or Max

[Bas Pels]

Undergravel filtration is based on filtration through the substrate. This implies the substrate must have some porosity

Corydoras require sand as substrate. You may add a few stones, and so on, but it must be sand - and sand has not much porosity. Therefore, for a corydoras tank, an undergravel filter will not work very well

Further, an undergravel filter will suck all dirt into the gravel - where it is hard to remouve. In my eyes, this is why an undergravel filter is among the worst possible obtions one can choose

You got a 60 gallon tank, and such a tank is certainly large enough to use an external filter. I'd say you should look for a filter filtering some 1000 l/hr (approx 300 gallons/hr), among which the Eheim pro II 2028 is in my eyes the best

These are easily cleaned, but will not require much cleaning. The first and second run will be soon, but after a while you will have to clean in only every 3 months or so

[Richard B]

It is really essential that Cory's are kept with a sand substrate - this rules out an undergravel filter.

Undergravel (or reverse undergravel) filters do provide a cheap efficient option for small & medium tanks but do have some limitations. I would never personally keep Corys in a tank with one though.

As Bas has said, an external power filter is a great option for this size tank - just cover the inlet with sponge to stop fry being sucked up

[Scleropages]

Further, an undergravel filter will suck all dirt into the gravel - where it is hard to remouve. In my eyes, this is why an undergravel filter is among the worst possible obtions one can choose

I completely disagree. If you have the undegravel filter set up for regular flow, it will suck all the debris into the gravel where it can easily be removed with a gravel cleaner (attached to a siphon hose or something like the Python system). On the other hand, if you have the undergravel filter setup with reverse flow, it will blow debris out of the gravel.

IMO, the fact that you can set up an undergravel filter with regular or reverse flow is pretty great.

You got a 60 gallon tank, and such a tank is certainly large enough to use an external filter. I'd say you should look for a filter filtering some 1000 l/hr (approx 300 gallons/hr), among which the Eheim pro II 2028 is in my eyes the best

These are easily cleaned, but will not require much cleaning. The first and second run will be soon, but after a while you will have to clean in only every 3 months or so

I disagree again. External canister type filters are a PITA. Relative to some other filter options, they are not easily cleaned. For a 55gal tank or larger, I like the Marineland Emperor 400 filter. You can fit two on a 55gal and have 800gal/hour of water movement. Much easier to change filter medium and clean than a canister filter. And, it is a fraction of the price of an Eheim. I've serviced all types of canister filters (Eheim, Fluval, Magnum, etc.) and they are all a PITA.

As far as keeping Corydoras, if you do not want to have sand as your substrate, you can use an undergravel filter with fine gravel. However, I would not recommend using the undergravel filter as your primary filter. I like to use them for increased water flow and oxygenation and for their great ability to keep the debris in the substrate where it is easier to remove come water-change-time.

[apistomaster]

There are so many factors to consider when choosing a filter and every filter design involves trade offs.
Undergravel filters are mainly dangerous in the way they conceal and do not remove wastes. It is true that very regular and thorough vacuuming of the substrate can control the accumulation of detritus but few undergravel filter users do enough substrate cleaning; out of sight, out of mind...

The Hang on the back power filters offer convenience of cleaning which is good because you have to clean them very frequently. They are cheaper up front.
They score poorly in efficiency as biological filters. They also require cut outs in the aquarium cover. Fish frequently jump out of these openings.
Many use proprietary filter cartridges which are expensive. Over time, the replacement cartridges can make life time operating costs many times higher than the reusable media most canister filters use. Just because a couple of cheap ones move twice as much water as a canister filter does not mean that they can come close to being as good as a canister filter flowing half as fast.

Canister filters are more difficult to clean than hang on the back filters but their bio-media and large volume of media used makes them score very high as biofiltration is concerned and they typically require less frequent cleaning.
Most aquariums will do fine if the canister filter is cleaned 4 times a year.
By any objective measure, canister filters are technically superior to undergravel and hang on the back filters.(I do not consider Marineland Magnums to be true canister filters.)

No matter which type or combination of types of filters you decide to use the most important things to do are do not overstock the aquarium and be sure to do large scheduled water changes.

[Scleropages]

The Hang on the back power filters offer convenience of cleaning which is good because you have to clean them very frequently.

Very frequently? Not necessarily. The frequency with which any filter needs to be cleaned depends on how quickly it gets clogged with particulate matter. I use Marineland Emperor 400 and Penguin 350 filters on all of my tanks and I would say I clean them 2-3x/year at most. Of course, they are helped by the undergravel filters I use. Also, I usually recycle the filter cartridges and can get a year out of them before they get thrown out. It's amazing how you can bring them back to life by rinsing them under a faucet.

Just because a couple of cheap ones move twice as much water as a canister filter does not mean that they can come close to being as good as a canister filter flowing half as fast.

Good for what? Moving less water, being a PITA to service, and becoming an anaerobic organism's dream when it gets clogged? No thanks.

Most aquariums will do fine if the canister filter is cleaned 4 times a year. By any objective measure, canister filters are technically superior to undergravel and hang on the back filters.(I do not consider Marineland Magnums to be true canister filters.)

Which objective measures are you referring to?

No matter which type or combination of types of filters you decide to use the most important things to do are do not overstock the aquarium and be sure to do large scheduled water changes.

I definitely agree--although the water changes need not be large. It is imperative to do regular water changes, but given the choice between frequent, small volume water changes vs. infrequent, large volume water changes, the former option is preferable in nearly every case.

[Scleropages]

I will say this in defense of canister filters--they will typically be quieter than a hang-on-the-back power filter. However, that is about the only advantage I can see for using one.

[MatsP]

I have 6 different canister filters, and the only time I've ever had any of them go anaerobic is when it's been switched off (either accidentally and by power cut). I clean mine about every 3-6 months (when the flow start being bad). Not bad at all.

--
Mats

[apistomaster]

Biological filtration efficiency depends on the surface area of the biological filter's media. Only canister filters and certain designs of wet/dry filters have optimal biological filtration capacities. Both happen to more expensive than hang on the back filters. You get what you pay for.
I happen to use both on my large display tanks.
Wet/dry filters have the edge over canister filters when it comes to keeping the dissolved O2 levels as high as possible for a given temperature.
The canister filters should be used in conjunction with at least an air stone because the do tend to consume some of the dissolved O2. They certainly do not function in anaerobic conditions; No commonly available aquarium filter does. Only the extremely complicated in both design and operation, denitrifying systems are meant to operate in anaerobic conditions and are the only means of creating a complete nitrogen cycle in a closed aquatic system. Denitrification uses anaerobic bacteria plus a chemical food source such as ethanol to break down the accumulated nitrates into nitrogen gas which is free to leave the system.
Any known aquarium filter design may be used but some designs are better at performing some functions better than others. One must know what the the limitations are for any filtration system and which filter does the best job for a given type of aquarium set up. Canister filters are a preferred design for those who are really into growing aquatic plants and use CO2 because the canister filters do not cause rapid loss of the CO2 injected as wet/dry filters do.
Their huge substrate surface areas available for biological filtration is undeniable.
No hang on the back filter design available comes close to matching the performance of canister and wet/dry filters.
Any review of the trends in aquarium filter designs shows how much emphasis there is on advancing the designs of wet/dry and canister filters.
This evolution of these designs would not be occurring if they were not regarded by experts as being superior to all others and if there were not a demand for such devices despite their expense.

Hang on the Back Filters long ago reached their full potential and they remain the cheapest option other than the now considered outdated under gravel filter design.

[Scleropages]

Larry, I appreciate your detailed response. For our discussion, I'd prefer not to mention wet/dry filters (with a separate skimmer box & sump) because I believe they are in their own category. I'd like to stick with hang-on-tank power filters and canister filters. As you mention, one will want to address the needs of the particular aquarium setup you wish to create when selecting an appropriate filter or filters.

I am in agreement regarding available surface area for nitrosifying and nitrifying bacteria in a filter--canister filters typically have a larger volume area for this than do hang-on-tank type filters. However, with exception of the Eheim Wet/Dry canister filter, I don't see any canister filters that have an intrinsic "dry" section. It is well known that these types of bacteria do well in a moist, rather than submerged, medium. So, with most canister filters, you'll have a larger surface area for the good bacteria, but not in the optimal environment. Hence why wet/dry filters were developed. Of course, with any canister filter, you can always add something like the Magnum biowheel to the filter output line to augment the setup.

Speaking of the biowheel, I'm sure you are aware that they are used on the hang-on-tank filters I mentioned. Now, I know that the surface area of those biowheels is nowhere near what you would find in a good, reef-ready wet/dry filter system, but they are there, nonetheless. It is true that this innovation wasn't something very recent in the hobby, but it does show some forward thinking in terms of developing this type of filter. I don't see how much more you can improve a hang-on-tank filter. And, why would you need to? If it is reliable and continues to keep your water parameters in good shape, why do you need to improve it? Why spend a lot more money on something that does the same job?

Now, when you go say something like this...

No hang on the back filter design available comes close to matching the performance of canister and wet/dry filters.

...I'll have to disagree. For a typical tropical freshwater tank between 20gal and 150gal that one might keep Corydoras sp. in, I would gladly match up an Emperor 400 vs. any canister filter (minus the aforementioned Eheim model--or the giant Eheim 2260) and save the money for some fish or fish food. Of course, in the 150gal tank, I would use 2 Eheim 2260's vs. 4 Emperor 400's.

Again, regarding the original question of this thread--if you want to use an undergravel filter, I would recommend you use it as a secondary filter. And, I would recommend that you don't think of it as a filter, but as a water movement device.

[MatsP]

To drag this thread back to the original subject:
After having listened to Hans-Georg Evers literally pleading for us to consider sand substrate ESSENTIAL for all Corys, I would say that this makes undergravel filters and corys unsuitable together - undergravel filters require large grains so that water can flow relatively freely into the filter. The grain size of sand suitable for corys will not allow enough water to flow through the substrate for an undergravel filter to work.

--
Mats

[Jools]

I will say this in defense of canister filters--they will typically be quieter than a hang-on-the-back power filter. However, that is about the only advantage I can see for using one.

Depends on what you use. I have three Eheim 2180 filters on 48x30x18" tanks that I have not had to change and they have been running nearly two years. One tank has discus, tetras and non-woodeating plecos and one tank has three big

Neosilurus

and a lot of larger and small rainbowfish.

I think the question was how do I best keep

Corydoras

and the answer is with sand. That means you can't use a UG filter.

Despite being unfashionable, I quite like UG filters driven by powerheads but I find cleaning the gravel is difficult if the tank is heavily decorated and has lots of plants and also you lose a lot of tank volume to gravel which, depending on bore and the method of powering the UG uplift, has to be between 1.5 and 4".

Jools

[Coryman]

Bunthid,

Putting aside the in depth discussions regarding the validity of all manner of different types of filters, I will try and explain why the substrate size used for under gravel filters is detrimental to the well being of all Corydoradinae Catfishes. It is simple really, Corys are primarily filter feeders, that is to say that they take up mouthfuls of substrate and separate any food particles in their mouths before ejecting the unwanted substrate through the base of the gills.

The barbels of Corys are sensory organs, primarily used for locating food, they also play a vital part in the mating process, but that is not the subject of this discussion. Having large substrate effectively changes the use of the fishes barbels, which are, along with the outer mouth parts, are then used as leavers and shovels to move the pieces of gravel around to access trapped food particles. It is this action can and often does cause the barbels to become tender and thus open to infection.

Another point that I feel needs mentioning is that only well washed river sand, sand used for swimming pool filters or childrens play sand, all of which are smooth grained and if looked at through a magnifying glass the grains look like tiny pebbles. Builders or sharp sand should be avoided at all costs.

Ian

Corydoras sp CW051 sifting through the fine sand substrate for food.

Image courtesy Ian Fuller & Corydorasworld.com