Filtration for Planted Aquariums – And How It Relates to the Water Cycle
Nature has its own natural water-filtration processes long before we humans tampered over it. From wetlands, which serve as natural kidneys that remove 20 to 60 % of metals in the water, trap 80 to 90 % of sediments from run-off, and eliminate 70 to 90 % of the water’s nitrogenous waste. It is essential to understand the functions of a good filtration for planted aquariums and our faunas, what it removes and what it retains, and the benefits/pros and cons of each type.
Riparian forests (forests adjacent to a body of water such as rivers, streams, lakes, pond, marshland, etc.) acts as biological filters that trap sediments, absorb and store excess nutrients, remove nitrogen and phosphorous composition in the water by up to 90 and 50 % respectively, and rectify the effects of the many water contaminants and pollutants carried by run-off from adjacent lands.
Before we dig deeper into the subject, it is imperative to understand the water cycle in nature. Hence, understanding how water quality falls and then gets purified/filtered by nature.
Table of Contents
Nature's Water Cycle
Are You Beginning to Correlate the Natural Water Filtration Happening in Nature with our Planted Aquariums?
So Plants and Soil can All do These? Do I still Need to Use an Aquarium Filter?
Types of Planted Aquarium Filtration
Can We Over-Filter a Planted Aquarium?
Nature’s Water Cycle
The Water Cycle or Hydrological Cycle are the processes that cycle the water from the ocean or a lake to the atmosphere, then back to land and ocean/lake again.
Now let’s explain the journey that water has to take. Water that evaporates into the atmosphere from the oceans/lakes will eventually condense and forms clouds. If the cloud gets too big and heavy, the water droplets fuse and fall as precipitation, mostly as rain, sometimes as snow or ice.
75 % of all water evaporated from the ocean falls as rain in the ocean again, mostly in the tropics. The remaining 25 % falls inland. Some water runs into streams, rivers, lakes, and marshlands, which also drains into the ocean. And some water is absorbed by the soil (infiltration) and becomes groundwater.
Some of the water is absorbed by plants and brought back into the atmosphere by transpiration. Just as animals and we release water vapor when we breathe, plants do too – but the term “transpire” is more appropriate rather than “breathe.” Some of the water is consumed by animals and humans too.
Studies have revealed that evaporation of water from the transpiration of floras leaves accounts for about 10 % of moisture in the air, with oceans, seas, and other bodies of water (rivers, lakes, streams, marshlands) providing nearly 90 %. To give you an idea of how much water plants can transpire: an acre of corn plantation gives off about 3000-4000 gallons of water each day, and a large oak tree can transpire 40,000 gallons of water per year. Wow!
Nature’s filtration/purification of water critically depends on the natural filtration, chemical absorption and adsorption of soil and organic matter, living things uptake of nutrients, and organic decomposition in soils and water environments. This means that soil, vegetation and bacteria, most especially in wetlands and riparian areas, play significant roles in the natural water filtration.
Absorption – is a process in which a substance permeates another, as in a liquid (water) permeates, or absorbed, by a solid (soil, for example)
Adsorption – is the deposition of molecules onto a surface. Adsorption occurs when molecules in a liquid bind themselves to the surface of a solid substance, like when clay, activated carbon, resins, or zeolites attract/adsorbs on their surface compounds/ions/contaminants/impurities in water purification systems. If you use one of these in your planted aquariums, they can remove some of the fertilizers you dosed for your plants.
Soil and rocks act as mechanical filters trapping debris, other free-floating contaminants, and sediments in the water. Soil can also absorb/adsorb harmful chemicals (chemical filtration), store nutrients, and grow bacteria that break down nitrogenous compounds (biological filtration). Vegetation absorbs nitrogenous compounds, too, and other excess nutrients in the water as well. In essence, plants act as biological and chemical filters (Ammonia, Ammonium, Nitrites, Nitrates, Phosphates, are chemical compounds, right?).
Are You Beginning to Correlate the Natural Water Filtration Happening in Nature with our Planted Aquariums?
Just adding live plants and soil where our plants can grow gives us another layer of different kinds of filtration in our aquariums. Not one, not two, but three, mechanical, biological, and chemical filtration.
Plants can even absorb these nitrogenous compounds with minimal or without any by-products (as long as they are healthy). We are just rewarded with lush growth and a very natural-looking enclosed ecosystem. The beneficial bacteria that colonized in our planted aquariums and within our filter after cycling converts nitrogenous compounds into other organic forms, ultimately into Nitrates, which is less harmful in non-elevated amounts (less than 40 ppm).
Nature Style Planted Aquarium Aquascaped by Fritz Rabaya Cebu Philippines
Another bacteria convert Nitrates to inert Nitrogen gas N2. Still, not all aquariums or planted aquariums can make these bacteria feel at home because they thrive only in an anaerobic environment, meaning an environment void of oxygen or too little oxygen. They can colonize in the deepest of substrate, oxygen should not reach it, and there should be no circulation of water in it.
Learn more and review about the Nitrogen Cycle here.
So Plants and Soil can All do These? Do I still Need to Use an Aquarium Filter?
We can choose to supplement these by using an aquarium filter, or you can choose not to (see the Walstad Method here, but the Walstad Method does not really forbid you to use an aquarium filter), but the function of an aquarium filter for our planted aquarium is not limited only to provide filtration.
- A suitably sized aquarium filter can provide the needed water flow or turbulence to distribute the nutrients and CO2 (if you are injecting CO2, prolonging the CO2 bubbles contact with water so it can be dissolved before it reaches the surface).
- Not just distributing nutrients and CO2. It provides the water current that some fish loves to swim against. Plants swaying with the gentle water current is a sight to behold.
- An aquarium filter can also provide the water surface agitation, aerating the water, for our faunas, and beneficial bacteria’s nitrification activities.
- It can also prevent the accumulation of wastes, sludge in the substrate, keeping them suspended/floating so they can be taken in by the filter’s intake.
Types of Planted Aquarium Filtration
The three types of planted aquarium filtration are:
They are all recommended, but a planted aquarium should have at least two, and in our experience, you should have both Mechanical and Biological Filtration. Chemical Filtration filter media like Activated Carbon, Zeolites, etc., is not much used in a planted aquarium. It will also filter out some of the vital minerals and fertilizers for our faunas and floras. Most of the filter types can house the filter media that will perform all these types of filtration.
Remember, your plants can do Biological and Chemical Filtration too. Plants can consume Ammonium, and to some extent, Nitrites and Nitrates. Plants also can home the good bacteria in their roots.
Mosses act as mechanical filtration trapping debris, uneaten fish food, detritus, etc. Just disturb the water near them, and those particulates will come out flying.
Filter Media – whatever your chosen filter is, it cannot do the filtration without the filter media. The filter is actually just the housing for your different filter media as well as pulling the water in from your planted tank, pass the water through different layers of filter media (providing mechanical, biological, or chemical filtration), and then push back into your tank by using water pumps.
We recommend buying a filter that doesn’t include any filter media so you can choose the most effective filter media available in the market that you can stuff in your filter (less cost). Some filter packages even include activated carbon, and you don’t need that in a planted aquarium.
This filtration will mechanically or physically trap floating solids from water passing through it, which is critical for your biological filtration’s efficiency. This includes fish wastes, sludge, detritus, uneaten food, dead plant matter, etc. The filter media for mechanical filtration should be inert – meaning it should not mess with your water parameters.
It is always placed as the first stage filtration of a planted aquarium. They come in many different forms, such as filter floss/pads, foams. You can even use polyester pillow stuffings (don’t buy those with flame-retardant chemicals), egg-crate foams, etc. They can be cut or molded to fit the dimensions of your filter.
They come in different porosities too, which limits the size of the particulates they can trap. They come in macropores (big holes, course), mesopores (regular-medium holes), and micropores (fine holes). Please see the hole-size comparisons in the image below.
Macropores can trap big floating solids but will allow medium to small ones to pass through. You should place the course mechanical media first in your filter.
The Mesopore ones can trap medium to small free-floating solids and should be placed next after the macropore mechanical media.
Last but not least, the Micropore mechanical media traps small to very small particulates from the water and should be placed last in the mechanical filtration section of your filter. The only problems with these micropore filter media are they can easily be clogged and significantly decrease your filter’s flow or turn-over rate. So I personally don’t use micro-pore mechanical filter media.
I only use one Macropore foam, two Mesopore foams, and lots of Biological Filter Medias in my Canister filter.
My Mechanical Filtration Foams after rinsing with extracted water from tank during water change
Mesopore – Green x2
Macropore – Black x1
To prevent build-up and clogging (reducing the flow of your filter and even stopping it), mechanical filter media need to be regularly cleaned. For example, I routinely clean my canister filter and my mechanical foam media once every 4 weeks. In other kinds of filters like a HOB or overhead filter, the mechanical media can be accessed easily and can be cleaned every week.
Filter floss and polyester pillow stuffings can be cleaned multiple times. Still, their structure deteriorates over time, gets clogged, and cannot release all the dirt anymore that it holds and needs to be replaced after a couple of months. Foams can last for months, and I never have to replace my macropore and mesopore foam for over 6 months until now. I am just rinsing it with tank water during water change, along with cleaning my canister filter every 4 weeks.
It is important that you rinse your mechanical media with old tank water extracted from your tank during water changes. Squeeze them several times to free up all the accumulated particulates trapped in it.
Your mechanical media also houses your good bacteria, and using chlorinated tap water to clean them is a big no-no.
Biological Filtration is a type of filtration in a planted aquarium where you will allow beneficial/nitrifying bacteria to colonize in your filter media to breakdown harmful substances in your water due to the Nitrogen Cycle naturally occurring in your planted aquarium. If you remember our discussion with the Nitrogen Cycle, go here, these harmful substances are Ammonia, Nitrites, and to a lesser extent, Nitrates.
Once the beneficial bacteria colonize in your filter media, it will get its food and oxygen from the water passing through them. When particulate matter gets into the biological media, clogging and decreasing the water flow in that area, it will starve that part of food and oxygen, causing the bacteria colony in that part to die. That is why mechanical filter media should be placed before the biological media.
Actually, these beneficial bacteria can grow on any hard surfaces as long as they are always wet, from your soil, rocks, driftwood, even the inside glass of your aquarium, inside walls of your filter, submerged equipment, and believe it or not, on your plants and their roots and some even floating in water (not that you can see it, except during bacterial blooms – excess beneficial bacteria floating, resulting to cloudy water or smoke-effect). Your whole planted tank is actually acting as biological filtration!!!
There should be an Ammonia source to trigger the Nitrogen Cycle to start in our planted aquariums. Now that’s a lot of beneficial bacteria if we can imagine the scale of it.
But don’t get me wrong here, the population of your beneficial bacteria depends on the amount of their food and oxygen available in your planted aquarium, not on how many biological filter media you put in your filter or hardscape that can home them. If there are no Ammonia sources, no bacteria will develop.
This means that your good bacteria colonies depend on how many faunas and plants you put in your aquarium that can provide them with organic wastes, decay, then release Ammonia, which becomes their food. For example, if you have a 20 gallons planted tank and have 12 Cardinal Tetras in it, the population of your beneficial bacteria will be proportional to the wastes produced by your 12 Cardinal Tetras and plants which produce less waste than other fish.
If suddenly you added 12 more Cardinal Tetras or 10 Mollies (which produce more wastes), this means that your beneficial bacteria is not enough at that moment. These Nitrosomonas bacteria that consume Ammonia can over-produce (reproduce quickly) during Ammonia spikes causing bacterial blooms. Cloudy water will result.
Once the correct population of bacteria colonized to overcome the Ammonia spike, the excess bacteria starve and die. That is when cloudy water will clear itself, that is, if you have enough biological filter media and hardscape to home them, or you have an over-sized filter with lots of biological filter media.
In a longed established tank, a bacterial bloom is less likely to happen. Any ammonia spike may be gone in 24 hours, even with a dead fish that you cannot see in a heavily planted aquarium (small only – otherwise, you will be able to see a big dead fish and can remove it immediately). Once the good bacteria have become established, they are difficult to destroy unless you mess with that balance using chlorinated water or any medications that can kill your beneficial bacteria or tank neglect.
That is why experienced hobbyists can get away with overstocking fish: their heavily planted aquarium, oversized filter, and biological filter media can keep up with all the wastes produced by overstocking or occasional ammonia spikes caused by a dead fish. The “1 inch of fish per gallon” stocking rule doesn’t consider a planted aquarium and a good filtration system that can keep up.
The filter media where our beneficial bacteria colonize should be inert – doesn’t mess with your water chemistry – and should have large surface areas (with respect to the bacteria’s size) and porous enough to house them (water passes easily through). This is a media that should not be replaced. When cleaning your filter, make sure that you keep your biological media always wet and only used tank water (after water change – tank water in a bucket) to clean/rinse/keep them wet.
Keeping my Biological media (crushed lava rocks) and mechanical media (foams) wet using old tank water during water change
Now let’s get back again with the mechanical media we discussed above. As I mentioned earlier, did you know that your mechanical media can house the beneficial bacteria too? It is also porous and can provide a lot of surface area for the good bacteria to colonize. So always see to it that you wash/rinse them with the same water from your tank during a water change, do not use chlorinated water.
Using chlorinated water will instantly kill your good bacteria that keep your planted tank established.
A variety of biological filter media is available for beneficial bacteria homage. From ceramic rings, ceramic or plastic bio-balls, K1, bio-home (sausage shape), Seachem’s Matrix, you can even go DIY by using plastic pot scrubbers (cheap alternative to plastic bio-balls), pumice or lava rocks (cheap alternative to ceramic rings or Matrix), or pool filtration sand (cheap alternative to K1 for moving beds in sump/fluidized filters for example).
Some biological filter media can promote both colonization of nitrifying and denitrifying bacteria. Which means they have both aerobic and anaerobic environments, respectively. Remember, nitrifying bacteria that break down Ammonia to Nitrite and Nitrite to Nitrate needs an aerobic environment (oxygen-rich). They will colonize on the outside surface of the media where plenty of oxygen-rich water passing through.
Different Kinds of Biological Filter Medias
Denitrifying bacteria convert Nitrates into inert Nitrogen gas N2 in an anaerobic environment (void of oxygen or very little) and can home themselves through inside crevices and pores of the media where little to no oxygen exists and no water flow.
Some examples of these are lava rocks, pumice, Seachem Matrix, bio-home, etc. I personally use lava rocks (a lot), some pumice that I picked up from someone else’s construction sand, 500 ml of Seachem Matrix, some ceramic rings from my old filter, and a couple of limestones to give me about 3 KH and 3 GH. Plus, the mechanical foam media I mentioned above are all squeezed in my Canister filter.
Chemical filtration is not often used or not used at all in planted aquariums. Activated Carbons, zeolites, and ion exchanger resins are the most common chemical filtration media and work by the process of adsorption, which I mentioned and described above in this article.
In the process of Adsorption and the effectivity of adsorption, the size of the particle being adsorbed is not only the factor. So our fertilizers, even in their tiniest elemental forms, can still be adsorbed by chemical filtration media.
They are detrimental to plant growth (most especially if used too long in stable planted tanks) because they will remove some of the fertilizer/nutrients you dosed for your plants and other minerals/ions needed for the biological functioning of our faunas. Activated Carbons or Seachem Purigen can be beneficial for newly started up planted tanks as they can adsorb excess dissolved organic waste and tannins.
Think about this, if you are using RO/DI water, the chemical filtration in your RO/DI water purification system removes even the good minerals for your faunas and plants, you have to remineralize the water before using and dose fertilizers for your plants, only to be removed by activated carbons again.
Activated Carbon in Pouches
The chemical method of filtration removes dissolved chemicals/compounds from the water via activated carbons, resins, and other adsorbents by attracting the contaminants in its vast surface area and pores. To give you an idea of how much surface area one teaspoon of activated carbon have: roughly an area of a football field! It can help maintain very clear water and remove the foul smell (if there’s any) in your aquarium.
Scavenging resins like Seachem’s Purigen hunts for only dissolved organic wastes in your tank water before they can even be converted into nitrogenous compounds when they started to decay (releasing Ammonia). It had no ill-effects on my plants when I used it. Still, I am not sure if it will starve my beneficial bacteria (didn’t use the Purigen long enough to test).
Activated carbons can remove chlorine from your tap water, but that should be the job of your water conditioner product, and you shouldn’t pour chlorinated tap water directly into your tank with faunas anyways.
Chemical filter media exhausts their capacity/effectivity over time, which means you have to reactivate or replace them.
Once they reach their capacity and are not replaced immediately, they can act as biological media. Still, they may leach a portion of the harmful substances they adsorbed back into the water.
One situation that you can use chemical filtration/activated carbons, for example, is when after treating your planted aquarium with medications to cure faunas illness or after you used algae medications along with water change. Remove the activated carbon after it has adsorbed the chemicals/medications after a minimum of 24 hours.
Another drawback of using chemical filtration media in a planted aquarium is – it may rob your beneficial bacteria of their food (if left inside the filter too long). Chemical filter media, such as zeolites, can readily absorb Ammonia. Activated carbon cannot. Ion exchange resins can remove ions such as Ammonium, Nitrites, and Nitrates, but these nutrients are beneficial for your biological filtration (food for your good bacteria) and your plants as long as they are not in excess.
Due to the atypical use of chemical filtration in our planted aquariums, we will not dig in further into this type of filtration. Remember, plants act as biological and chemical filters in our aquariums, too, so no need for chemical filtration.
Can We Over-Filter a Planted Aquarium?
Have you ever heard of over-filtering a planted aquarium, or rather an enclosed ecosystem? While we can’t really over-filter a planted aquarium, it so easy to under-filter it. If we are talking about biological filtration, there is no such thing as “too much biological filtration.”
There is no such filter or combination of filters that can make your tank immaculately clean. Since there is no running water as we have an enclosed ecosystem, wastes are constantly produced and stay in the aquarium.
It is hard to starve your beneficial bacteria of their food (Ammonia, Nitrites, Nitrates) unless you mess with it. Wastes and organic matter don’t just magically turn into Ammonia. It still needs to decay and will release proteins, enzymes, dissolved organic compounds, acids, etc., into the water. Unless you are water changing every 2-3 hours, but why would you do that?
Clearwater is not hard to achieve once your planted tank is established and balanced.
Here are situations where there can be over-filtration, or should I say the wrong choice of equipment, or over-zealous attempts to provide too much water surface agitation and water circulation, or too many equipment:
- (not a filtration problem per se) Too much water current might stress some fish, plants are being uprooted, or it looks like you have a hurricane inside your planted aquarium, etc. Small fry, shrimps, and snails can be sucked in by the powerful filter intake grids (you can put a DIY foam around the intake though to prevent this), choosing too strong a filter for a nano tank.
- Using chemical filtration media, which are detrimental to plant growth, may starve your beneficial bacteria in a planted aquarium.
- Using too fine mechanical filtration drastically decreasing the turn-over rate and effectiveness of your filter.
- For fluidized filters (moving filter media beds in a sump filter), if too effective, may starve any filter feeders (you can feed them, though)
- size and space – you need enough space within and outside your tank to fit the filter/s, intake, and outtake, other equipment (pumps, wave-makers), etc. Each filter type has pros and cons, which we will discuss in the next article. Some can be an eyesore in an otherwise pleasant aquascape.
Personally, I always prefer an oversized canister filter that can house a lot of biological media with a minimum of x10 tank volume turn over rate. For example, I have a standard 35 gallons planted aquarium, so I would choose a minimum of 350 gallons per hour (gph) canister filter like the Sun sun 303b that I am currently using (rated as 370 gph). The manufacturer rated the canister up to 100 gallons tank.
My Canister Filter at Lower Left
This was why I got away with overstocking of fish (my Platies bred profusely started only with 3, and they blew into 40 +). My oversized canister kept up with all the wastes produced at that time frame. An oversized filter (any x10 gph turn over rate filter based on your tank volume) will work much efficient, and they will be able to take unexpected/emergencies like Ammonia spikes (e.g., dead fish) without the tank parameters even noticing it, plus my tank was heavily planted from the start.
As we dig further into the intricacies of a planted aquarium, we had just discussed the correlation of Nature’s Water Cycle and its natural filtration systems into our planted aquariums.
We also discussed another importance of soil and plants in an aquarium. They introduce another layer of natural filtration types: Mechanical, Biological, and Chemical filtration.
We also covered in-depth these types of filtration that we can utilize in our planted aquariums. They are all recommended, but a planted aquarium should have at least two and the most important: Mechanical and Biological. Filter media for both should be inert.
We also outlined the different filter media for both that we can use and added cheap and DIY alternatives.
Whereas Chemical Filtration in a planted aquarium is seldom used due to the reasons that they will remove necessary minerals for biological functions of our faunas and plants as well as fertilizers. They can also possibly deprive our beneficial bacteria of food by removing nitrogenous compounds if we left them long enough in our filter.
Finally, we touched on the idea of over-filtering our tank and provided some situational drawbacks of doing such. We also provided recommendations using an oversized filter and its requirements.
An oversized filter (any x10 gph turn over rate based on your tank volume) will work much efficient, and they will be able to take unexpected/emergencies like Ammonia spikes (e.g., dead fish) without the tank parameters even noticing it,
I hope you enjoyed this article and if ever you have additional questions or want to share your experiences with filtration for planted aquariums, please leave a comment below. We hope this article helps you decide what should be the filtration types that you want to include in your filters and choose the best filter media for your needs. Next, we will be discussing the many different types of filters that you can use in your planted aquariums. Each has its pros and cons, and we will help you decide what is best for your needs and what to look for when choosing a filter.