ALL credit goes to Sergio
for writting this. FROM AQUABID FORUM.
-The bigger the tank the better, but you can have a nice unfiltered tank in as low as 1 gallon if you are very careful
-Use the best lighting you can provide without incurring huge costs (two strips that span most or all the length of the tank are ideal)
-Use a natural substrate, gravel works well but if you want to give it a try use soil (very clean of chemicals of course)
-Plant as many species of resistant plants as you can while letting each get some light (the more species the more likely several will become established and they would absorb any compounds in the water)
-Use floating plants, I think floating plants act as my filter, there are several species (again a mix is ideal so you can keep the ones that establish well in your particular settings). You have to keep removing them to let light get to the other plants in the tank, always remove the ones that are looking the worst, at some point all of them will look nice, in which case just pick some and remove them. If you remove most of them be careful to put any snails or eggs that might be on them back into the aquarium.
-Have tons of fast reproducing snails, ramshorns or pond snails are ideal. They help keep the algae under control and eliminate any type of extra food that might be around
-Do a nice cycling, I recommend setting the gravel and plants, adding one pleco wafer of 3/4 inch diameter and all the snails, that will give a fast start. If you have an already established tank fill the new tank with water from the old tank. After the snails finish the food add another wafer and do so for a while before adding fish or other invertebrates. If the wafer goes bad leave it there to decompose (unless is a very small tank in which a food pellet might be a better idea)
-Under-stock your tank. I am a big advocate for keeping only species that can breed in captivity, which are also ideal in this case since you can start with only a few individuals and let their population grow. Unless you are never adding food (which I only recommend in very big tanks and for very advanced hobbyists who can really estimate that their tank will produce enough food for all the fish and invertebrates in it) the population will eventually be too big, so keep taking individuals out when it seems necessary.
-Do not overfeed too much. This is kind of obvious but it is even more relevant in un-filtered aquariums. A bit of overfeeding however won't do any damage as long as you have lots of snails.
-Unless you feel like its very needed don't do water changes, and always do small ones (max 25%) when you do. If you set up everything alright you should never need to.
-Never vacuum the substrate. The dirt that accumulates helps maintain a healthy bacterial community to keep thins in a nice equilibrium. If there is too much dirt (to a level that you deem a problem) vacuum half of the tank. You can vacuum the other half again a week or two after, but in general don't vacuum.
-It is likely, and probable, that you will have green water at some point, do not worry, its quite good to establish small invertebrate communities, the fish don't mind it, and eventually it will go way (specially with the floating plants)
-Most of my experience is with softwater low pH tanks. Although most things apply in any case it might be harder to achieve with hardwater high pH tanks since several compounds are more toxic to fish at higher pH. This justs means you have to be more careful with the cycling
-You have to have plants, otherwise you might need to do water changes way more often (from about never to every some time) and will certainly have algae (just algae might be enough in some settings though)
A hypothesis on how it works:
I haven't done the appropriate experiments, nor do I know of data around good enough to support it, but I will try to make sense of this by providing a set of ideas on how I think it works.
-The carbon cycle can be easily thought of as a good equilibrium between CO2
exchange at the water interface, while the plants produce more O2
than they consume (they do consume at night, I have never heard of an aquatic plant capable of CAM metabolism, which allows for CO2
fixation at night) on a day's average, and the animals simply consume oxygen liberating CO2
. Only rarely have I seen symptoms of a lack of oxygen in the fish in unfiltered tanks, and it was only when the tanks were overstocked (In general is good to keep the tanks understocked). There is also a microbial component in which bacteria consume decaying matter, which for this purpose makes them the same as animals. There might also be some anaerobic bacteria as a part of the cycle, in which case there might also be a release of methane to the atmosphere.
-The phosphorous and micro-nutrients cycles are also very simple since all of them get in the water only by the input of food you provide (I normally don't use fertilizers of any sort), and get consumed up by the plants and algae, which might in turn go back to the animals if they are not strict carnivores. There should also be some accumulation in the gravel but I have never had an issue with it. Eventually all of these nutrients go into the plants and since the only maintenance regularly needed for unfiltered tanks (at least as I keep them) is to trim the plants, they go out of the tank as components of their tissues (or as fish tissues if you are breeding and have to, at least at some point, move the new fish to a different tank).
-The nitrogen cycle is I think the harder to explain, basically in a filtered tank you remove a certain amount of nitrogen every time you change the filter media, since a lot of bacteria lives there and there is also some chemical retention. This means in the unfiltered tank you will have that "unknown" amount as an excess. That can be solved in several ways, one of them would be for the plants and algae to absorb more, which is likely (although they might be CO2
limited as most aquarium plants are, so they would not be able to absorb that much). There is clearly a community of microorganisms in the substrate which takes up a certain amount. The fact that the fish don't die, and actually live quite well, means that the nitrogen must be processed in one way or another. I am inclined to think that a certain level of de-nitrification might actually be occurring. In this case some anaerobic microorganisms (mostly bacteria I would guess) are producing nitrogen gas, which simply goes to the atmosphere. I have a few observations of methane production which implies anaerobic conditions, so I think de-nitrification is likely to happen (nitrogen gas has no smell so I could not detect it as the methane, you can see sometimes tiny bubbles coming up randomly from the substrate, if you get close enough you can smell the methane, which is in minimal quantities so it shouldn't be a worry). It happens in the substrate, in the lower layers, where there is enough accumulation of debris to create an anaerobic environment. It should be quite a good thing for the tank, since it would remove some nitrogen. There have been cases in lakes where it has not been a good thing since the accumulates gases came up all at once killing everything on its way, but given the scale of a tank that should never be an issue (if you see a truly big bubble, like more than an inch in diameter, forming in your substrate just don let it become huge, help it out and that would do it).
How the idea started for me:
I had kept tanks for a very long time, and always relied on hang on filters, because I like their ease of use, and I think the movement of water they provide is good enough for aeration so I do not use anything else. Out of laziness and to save some money I starting slacking off and not changing the foam and activated carbon with the recommended frequency, and noticed that the fish were doing fine. After that all I do for maintenance of hang on filters is to rinse the foam throughly, and change it whenever it becomes too clogged. I noticed that over time my tanks pH would go down, until it stabilized around 5.5. Fish would do fine like that and all I needed was a water change of 25-50% a month, although sometimes I would go for 3 months without one. This was in a tank with a couple of silverdollar-like fish (don't know the precise species) an eight banded leporinus (Leporinus octofasciatus
) a midnight catfish (Auchenipterichthys thoracatus
) and a baby silver arowana (Osteoglossum bichirrosum
). It was a 50 gallon, no plants, and was stable with the fish growing nicely for a long time until I had to give it away when moving to the US (I was in Colombia), well except for the arowana that jumped out at some point. It had some slow growing brown algae on the glass, harmless to the fish, and I would only remove it from the front of the tank since I consider algae quite beneficial.
Anyway while having that tank I had several others and I like planted thanks but kept very simple lighting ( a normal incandescent lamp but with a 60 watt fluorescent bulb). I kept two tanks a 29 and a 10 gallon, with just that one bulb on top, and some window light. As you can expect very few plants grew like that (plus the Colombian aquarium market is not good for plants), but I found that pondweed (Egeria densa
), needle sagitaria (Sagittaria subulatta
) and a plant I haven't been able to identify with certainty, but that I suspect to be a variety of dwarf hygrophyla (Hygrophila polysperma
) grew quite well. I decided that to keep the plants at their best it might be a good idea to try soil instead of gravel as a substrate, but since soil is so messy I knew I needed the minimum water movement possible so thats how I started my first un-filtered tank, a 1 inch layer of soil (from my garden) a lot of needle sagitaria, some pondweed and one amazon sword plant (Echinodorus amazonicus
) that I got at the time and did quite well. It was an open top tank, and it thrived with all sorts of tiny organisms and pond snails too off course, which seemed to make my fish quite happy. I started using it as my breeding and raising fry tank (I got into breeding bettas, gouramies and paradise fish then). I then did the same with my 29 gal
, which also had some driftwood in it. In it I kept about two dozen cardinal tetras (Paracheirodon axelrodi
), a few rosy barbs (Barbus conchonius
) a bristlenose pleco (Ancistrus sp.
) and a few wild guppys (Poecilia reticulata
) selected for being the nicest out of my feeder ones.
At the same time all of this was happening I had the opportunity to travel a bit in the amazon area and was surprised at the conditions I could find some tetras living in. They would be in tiny streams, which is fine anyway you think of it, but the surprising thing to me is how they were unaffected by a heavy rain which would as a minimum triplicate the volume of the stream, taking all sorts of secondary plant compounds with it and having a very different temperature. What I learned from that is that fish are in general way tougher than thought. After that I never did any checking of my water for a water change as long as it was 30% or less of the total volume (even though the pH of the fresh water was 7.4 and the one in my tank 5.5). Never had any issues with that.
I moved to New York City a little more than a year ago, and as always ended up with lots of tanks. I have my 29 gal
with no filter, lots of light (for me at least, that means two 15 watt strips), I have tons of ramshorn (Planorbis sp.
) and pond (Physa cf. acuta
) snails, a few livebearing Japanese trapdoor snails (Viviparus malleatus
), a established community (they are breeding and I think its stable or growing) of cherry shrimp (Neocaridina heteropoda
), a few golden clams (Corbicula fluminea
), which I take to mean the quality of the water is great since they are filter feeders and haven't starved in about 7 months, and some very nice lotsoffish endlers #2 (Poecilia wingei
). The tank has tons of plants and I never do water changes on it, although I take water from it to fill any new tank I get or my betta bowls which in the end means I do very small water changes at least monthly and sometimes weekly, of about 5% or less). I also have a pair of bristlenose plecos (Ancistrus sp.
) I got on aquabid, and they are breeding like crazy (I'm on the third span). I decided to put a small bubbling line with all the babies just in case, although I think it doesn't really make a difference. I tested that since the first appearance of this article and it does not make a difference. I had already bred bettas (Betta splendens
) and dwarf gouramies (Colisa lalia
) in there and a US native the bluefin killifish (Lucania goodei
) although sadly the adults and then the offspring (of which I got 8 to adult size) started predating heavily on my shrimp (to which I am very new) and died when I moved them out of the tank. I like breeding in these types of tanks and following a more "natural" course, which means only a few fish will make it since they are competing for the live food available (Not to say in some cases I don't use other strategies, I am breeding bettas in small containers and feeding several types of special foods right now). The tank has several pieces of cholla wood and two pieces of driftwood. For quite a while (about its first 3 months) it had green water, which although bad for me is quite good for the tank (specially for my filter feeders), but it eventually stabilized. I have to say though the green water kept a bigger community of tiny organisms which was way better for breeding (now from a dwarf gourami span I get about 2 fish out, that unless I leave the tank with no fish for a month and then put the eggs in). In that tank I have amazon frogbit (Limnobium laevigatum
), small water lettuce (Pistia stratiotes
) and salvinia (Salvinia cf. natans
) on the surface, they grow amazingly fast and I have to keep giving some to my friends (I seem to end up always getting all my social circle into aquariums one way or another), and hopefully soon placing some auctions for it. Those plants are definitively the best filter one could have. The tank has also a population of scuds although its hard to tell how stable it is.
The only other un-filtered tank worth mentioning is a 5 gallon, I have had it since October last year, it has several plants as well as some blue shrimp (Neocaridina heteropoda
) which are doing nice since their population is increasing, only has ramshorn snails (Planorbis sp.
) since I like keeping some tanks with just one species just in case in my mixed tanks one out-competes the other, and two of my bristlenose pleco babies. The tank is it by a 10 watt fluorescent bulb on an incandescent fixture. It has no aeration or filtering of any sort. I have a pair of Betta rutilans
there, sorry I don't know the common name for it. I am trying to bred them and so far have failed. I have to say I don't even know what they eat, water fleas (Daphnia magna
) will last a few days in the tank, sometimes weeks and I think they eat some but very sporadically, the shrimp numbers are slowly growing, so if they eat them is only rarely, and the only thing I know the female eats for sure is dero worms (sorry don't know what they are, they are also called microfex). I have done two 50% water changes since I started the tank, the first one replacing the water with water from the 29 gal
, the second one with fresh water, but only to try to induce them to breed. It is a very nice unfiltered tank for sure.
I failed to mention my tanks here all have gravel so far, even the 29 gallon for which I made the mistake of buying some black gravel that wasn't naturally black but quartzite derived gravel with some coating, that made the thank very unstable I highly recommend always using natural gravel. On a side note on substrates if you are curious about the soil substrate I highly recommend trying it in a 10 gallon with good lighting. I suggest you read the book "Ecology of the planted aquarium" by Diana Walstad. Although I don't think all the conclusions she draws from the published research so far are justifiable (not because they might not be true but because the data is not enough to support the conclusion) it is the only book out there with that sort of coverage and is definitively worth reading.
Ok I think thats it, I hope I didn't forget anything important. A lot more people has experience with this type of tanks so I'm hoping they complement anything I said here.
I think of myself as a relatively experienced aquarist (I have kept tanks all my life, although thats not that much, I'm a PhD student) but I am not an authority. I am a biologist and microbiologist and although my research has not been directly on aquatic ecosystems I have worked a lot in ecology of tropical forests and been part of some research groups in aquatic environments. What all of this means is that the information you could gather here is correct to the best of my knowledge, but if something doesn't work precisely as I claim it does you have to take it easy on me, and please be critical when you apply it. I wrote this article because when I introduced myself some people were interested in what I do and I want to start a discussion on it, hoping to help some with what I know and learn a lot from the experience of others.