Look:
Don’t let anyone tell you undergravel filters can’t be an effective filtration option for your tank.
When done right, they can be POWERHOUSES for stabilizing a healthy aquarium.
Granted:
The traditional undergravel filter setup method is straightforward:
Plates on bottom.
Gravel on top.
Water pulled down into the gravel bed.
BUT…
There are some pretty major drawbacks to this setup (which is partly why they have fallen out of favor in recent years).
- Gunk gets trapped in the rocks and under the filter plate. Not only is it hard to clean, but actually, this can be a very dangerous problem – especially if not cleaned very frequently. As in, all. The. Time. These pockets can become anoxic and nasty disease-causing bacteria can form in these areas, leading to sick fish. Even if you vacuum out the gravel frequently, you still can have all this debris lodged under the actual plates that can’t come out without a deep cleaning – sometimes necessitating a tank tear-down. 🙁
- Small gravel poses a choking hazard for some fish like goldfish. Bigger or adult goldfish especially are prone to getting “rockitis” where the gravel actually gets lodged in the back of their throats, blocking their ability to eat and causing other symptoms like lethargy and strange mouth movements.
- Difficult to grow plants in directly. Plants can grow roots into the filter plates and restrict the water flow through the filter, destroying the effectiveness of your filtration. If you want rooting plants it’s recommended to keep them in something like a glass plant jar.
I’m not saying never ever do it this way or it’s the end of the world if you do.
But I think there are some better ways that will make your life easier and keep the risks down for your fish.
My motto?
Fishkeeping should be as simple as possible.
So today I’m going to share the top 2 ways to set up an undergravel filter that overcome both of these problems – and make your biological filtration MUCH more efficient in the process!
- Related Post: Do Goldfish Need Gravel?
How to Set Up a Safer, Easy to Clean Undergravel Filter for Your Fish Tank
I’m giving you the 2 best methods I know of.
There may be others I haven’t tried that are just as good or even better.
Also:
Don’t be afraid to get creative and experiment if you want.
For what it’s worth, I really like the Penn Plax line of undergravel filters as they can be customized to fit almost any dimension of tank.
You can also piece together several smaller sizes if your aquarium has a unique footprint.
Whatever works for you 🙂
You can use the setup designs below alone or in conjunction with another kind of filter.
The Sand Cap Method
This is idea combines the benefits of sand (does not trap muck like gravel) with the efficiency of undergravel filtration.
I recommend using CaribSea aquarium sand, the Crystal River style.
Out of all the sands I’ve tried, this one works the best.
Why?
The grain size is much larger than average sand but still small enough to prevent fish choking while having the debris sit on top, patiently waiting to be vacuumed.
One big advantage of this method is you don’t have to deal with plants rooting in the filter plates, which is a big problem for growing plants with traditional UG filter setups. Due to the strategic placement of the polyfiber barrier, this method is ideal for keeping rooting plants.
I highly recommend adding some heavily rooting plants as it will keep the substrate aerated and help lock down the gravel-type media under the sand for those with digging fish.
Not all plants enjoy soil aeration, but some like Amazon Swords really do.
The roots cannot get through the barrier and block the flow – but the water can.
The barrier is not thick enough to serve as mechanical filtration, and even if it were it is far down below the layers of sand and gravel-type media. This means it does not need to be replaced continually.
- Place your assembled undergravel filter plates on the clean, bare bottom of the aquarium. If your tank is already set up it is a good idea to do a thorough vacuum and water change. You will need an air pump and airline tubing to run the airstones in the filter. I use the double outlet airline pump as you don’t have to T off the airline tubing and you only need to use 1 outlet to run it.
- Cut a piece of thin polyfiber padding to fit over the surface of the plates. This will ensure no fine debris or sand can work their way down underneath the plate and get nasty over time. I used an Imaginarium thick polyfiber pad torn 3 thinner layers and spread them on the filter plates, snipping a slit in the fiber where the uplift tubes connect. It’s ideal because the structure allows a lot of water flow while preventing sand and debris from entering. You don’t want to use something that will break down over time, like a cotton cloth.
- Pour a 1/2-1″ layer of gravel, pre-soaked Seachem Matrix or crushed coral (for hardwater fish like cichlids) over the polyfiber. This will help with water circulation as well as provide additional surface area for biological colonization. If you use crushed coral or another porous substrate, you can also provide an area for denitrification (aka nitrate reduction) to occur which would not happen with gravel. On top of this layer (optional but not manditory) you can place a layer of mesh or gravel tidy to prevent this layer from intermingling with the sand.
- Pour a 1.5-2″ layer of sand over the gravel. If you have digging fish you will want to use about 2″ to prevent them from disturbing the gravel underneath.
Some tips:
Most UG filters come with little carbon inserts you can put on the tips of the uplift tubes.
If you’re like me, you find this unsightly.
Part of why I love Undergravel filters is because they are just about invisible, and I don’t want distracting little black squares in the tank (third world problems, right 😉 )
So where do you add other kinds of media (maybe Phosguard, Purigen, Algone, active carbon, or otherwise?)
With this particular setup it isn’t really that easy – as in, pretty much impossible – to push aside all the stuff on top of the filter plates and bury your packets of chemical filtration like it would be with a regular undergravel filter setup.
And if you have plants rooting – forget about it.
But there’s a workaround:
I use this little internal power filter just big enough to put my chemical filtration in, stuck behind a rock and plants. It doesn’t have to be huge, as it’s not functioning for biological filtration (you are more than covered on that!).
Yes it gives you another black cord to deal with, but hopefully your tank is planted enough that the stems and leaves can conceal it.
The Reverse Flow Method
Reversing the flow has some major advantages (source).
Here’s how to do it:
- Place your assembled undergravel filter plates on the clean, bare bottom of the aquarium. No need for the airstones here.
- Pour a layer of gravel or larger porous filter media (such as Seachem Matrix, Pond Matrix which is a bit larger than Seachem Matrix, or Hydroton). You can also use larger river pebbles, though these may restrict the water flow more and won’t support nitrate reduction.
- Use a submersible powerhead to force water down the uptake tubes. This is what reverses the flow and pushes water up through the substrate rather than forcing waste down. Pumping water through the substrate upwards keeps it free of mulm-buildup, which can cause deteriorating in water quality.
- Install a prefilter on your powerhead to prevent debris from being pushed by the powerhead underneath the filter plates. This is really a must or you will end up having the same problem as a regular undergravel filter setup.
It’s a good idea to supplement this method with an airstone, sponge filter or HOB filter for aeration and surface movement.
Bonus:
Connect it to a canister filter packed with mechanical filtration media to purify the water first before it sends the flow down the UG filter tubes from the outlet.
Hello, sparkling clean water!
Advantages of Undergravel Filters
Quiet
Annoyed by loud sputtering, gurgling, trickling or dripping from other kinds of filters?
The only noise just about will be coming from your air pump vibrating (if you use one).
If you work in an office or want a quiet tank in your room this can be a big perk.
Invisible
Just about every filter out there is an ugly intrusion into your beautiful aquarium scene.
There’s almost no way to totally hide most of them.
With Undergravel filters, you integrate the filtration so closely into the aquatic environment there is almost no transition.
Huge biological footprint
You can’t beat the surface area the size of your aquarium’s footprint.
End of story. 🙂
Substrate Aeration
Prevents bad anaerobic forming in the substrate when set up using the methods described above – score!
It’s okay to go heavier on your layers of substrate since you are getting oxygenation happening.
Conclusion
I hope this post sparked your interest in the possibilities of filtration with undergravel filters.
What about you?
Have you tried them, and what have been the results in your tank?
I’d love to hear your experience in the comments below!
Can you leave the UG Filter untouched forever or will you eventually have to breakdown the aquarium for a thorough cleaning?
With either method you don’t need to break it down to clean it as gunk cannot build up underneath it.
I am thinking of switching my 120 gal salt water tank to fresh water. Already use an UG filter with 4 power heads and an external Marineland Penguin Power Filter w/ Multi-Stage Filtration (350gph).
I find the sand cap method very interesting, especially for the growth of plants.
What do you think about setting up the tank the sand cap method for normal flow and from time to time switch to reverse flow using the pre filter as mentioned? Would the reverse flow have any affect growth of plants ?
Thanks, Ron
I have never tried that but it would be a fun experiment! Most plants don’t like undergravel filters of any style so you might want to jar them.
What exactly does mating mean?
Sorry I ment jaring
Using glass jars filled with dirt and capped with gravel, I do it in tanks with substrates not specifically for plants
I have a question, cycling a tank with this filter is any different than the cycling with the other filters?
Cycling all filters is generally the same.
I have used an under gravel filter very successfully in a 2 foot tank of tropical fish for many years. I do regular part water changes and yes I do break down the tank completely every 18-20 months which I don’t mind as I have a chance to redesign the whole look of the tank while the fish wait patiently in buckets.
I do find these methods interesting in regard to plants as that’s the only thing I sometimes have difficulty with. Thank you for such good information, I’m definitely going to try this!
Thanks for sharing your experience, Peter!
I would love to set my new tank up correctly using the reverse flow under gravel filtration. I bought a used tank set up for my daughter for her bday…it is 20 gallons with a top external filter and also came with an underground filter with 2 large tubes with the old charcoal pieces stuffed in the tops of them. It has a heater, plenty of gravel, stones, and plants. We rinsed everything, filled it with water and have the top external filter and the heater running and are letting it come to temperature before doing anything more. I have read all I can find on how to use the underground filter in reverse, but I still cannot understand what items I would need to purchase in order to actually set this up. I’m also trying to figure out the best way to add lighting as there is no light with the setup currently. I looked at the linked powerhead but in the photos it appears to be pulling water up from the tube rather than pushing it down the tube. I understand we would need two of them if this particular powerhead is the correct one and is capable of blowing air downwards through the straight end. Our budget is limited. Does anyone have product advice?
So when you plug the pump in, water will come out the gridded part of the pump. That’s what you insert into the UG filter tubes so it blows the water down the tube and into the filter plates below. You may have to use another piece of flexible tubing to attach it so it fits snugly and is the right size. Hope that helps 🙂 For lighting, you can find pretty affordable units on Amazon. It doesn’t have to be fancy if you aren’t growing plants. Something like this would work well.
Thank you so much for responding! I have so much to learn about this. Would a two pack of the 350 pumps here
https://www.amazon.com/Aquaneat-Powerhead-Submersible-Undergravel-Hydroponics/dp/B07L3FHCYY/ref=sr_1_13_sspa?keywords=aquarium%2Breverse%2Bpowerhead&qid=1564130210&s=pet-supplies&sr=1-13-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVExXT05WMDYzMU5UJmVuY3J5cHRlZElkPUEwMDczMzYyMzg2WVlJSlZaVTFHMiZlbmNyeXB0ZWRBZElkPUEwNjM4NTMyMldLS003VjgxNzA1SyZ3aWRnZXROYW1lPXNwX210ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1)
work for the reverse flow of this brand? You mean the part at the very bottom that is sticking down and has gridded lines in it will be stuck down in the clear tubes coming up from the undergravel pump? How can I know if the water will be pushed down or pulled up from that section of the pump?
2 350gph pumps might be a lot for a 20g. I’d probably stick with the 60’s. But that style of pump works fine. Yes, the bottom tip that has the cage goes into the tube. That’s where the water comes out. It will push it down into the tube.
Ok, I just saw your reply! Thank you again! I am going to get these ordered and set it up with the two pumps going into the two large clear tubes.
My undergravel filter two about 1 inch wide clear tubes coming up out of the back side of it. Will I need two pumps, both of them the long slotted point of the pump pushed down into the tubes? I was thinking that part of the pump pulled in water rather than pushing it out. Is there something I need to do to make that happen? Sorry for the confusing questions I just don’t understand exactly how it works.
Yes you will need two pumps. The slotted part is pushed into the tubes. You may need to use flexible tubing to connect.
This is very helpful! Using the sand cap method, how much seachem matrix will I need for a 20 gallon tank? I’m trying to figure out how much to buy. Also, if I choose to use the little internal filter for chemical filtration, do I need to buy the one for a 20 gallon tank or can I use a smaller one since I am combining it with the under gravel? Lastly, can I use fluorite sand for plants with an under gravel filter? Thank you!
I would get 3 of the big buckets, though of course it depends on the thickness you are going for. You can use a smaller one, the Penn Plax 300 would be fine and is the one I use. It pumps 100gph. I don’t see why you couldn’t 🙂
Hello, I’ve been running my UG filter (not reversed) for a couple months now and give it three water changes a week while dosing it with the bacteria cleaner you recommend. I’m still a bit worried about those pockets of toxins everyone talks about though. Is there any way to test or just know when those pockets are forming to help prevent them? Thanks.
If you are running a UG filter, there is very minimal chances of HS buildup. The smell of rotten eggs is the indicator.
Where do I attach the pre filter sponge in powerhead in reverse method?
You would attach them on that grid part, the intake of the power filter. The water is not sucking up the undergravel filter tubes, but rather, being forced down, so the intake is left open. Hope that makes sense.
I have africans Id like to try sand cap method. Does tge sand allow sufficient water flow to the UGF?
Also would it be possible to use the grey high quality lanscaoe fabric instead of poly fiber?
Great article and idea tganks!
It seems to do so when I tried it. Never tried that fabric but you certainly could experiment!