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Here's an interesting conundrum I alighted upon a few moments ago. I thought I'd run this past everyone and see what resulted.

Ordinarily, there is an upper limit to the number of fish that can be kept in a given aquarium. This upper limit is not merely affected by mere numbers of fish, but also such factors as adult sizes of the fish, and whether or not those fish species in question have territorial requirements (e.g., Cichlids). so, for the purposes of this conunudrum, I'll leave out big and territorial fishes, and concentrate upon species such as small Characins and Corydoras.

Assume that I set up a 4ft aquarium. And that in this aquarium (once the filter is matured enough of course!) I put in, say, 12 Cardinals, 12 Lemons, 12 Rosies, 20 Pandas and 8 Otocinclus. it's fairly crowded, but assume I've invested in a decent filter setup so that this collection doesn't foul the water too quickly, and that I'm diligent with my water changes (my usual twice weekly régime as practised on the current Panda Fun Palace&#8482.

Now, I suddenly have a brainstorm.

I connect the 4ft aquarium to another 4ft aquarium out of sight somewhere, thus doubling the water volume available to the fish (and also facilitating easier water changing). Which I set up as a vegetable filter/refugium for assorted critters including Gammarus shrimps that I use as live food for the fish.

Under such a revised setup, would it then be possible to bump up the Characin shoals to 16 each, and add an extra 4 Pandas?

I've used specific numbers and specific fish species choices here, but the basic question is this: would attaching a refugium of comparable volume to the original aquarium allow increased stocking? And if so, by how much?

A little puzzle for you all to contemplate.



Panda Catfish fan and keeper/breeder since Christmas 2002

That is an interesting cunundrum...

After thinking about it bit, however, I'd have to say that even though the water volume would technically allow for greater bio-load, the space probably wouldn't. Even though you're talking about small schooling fish with little to no aggression or territoriality, I would think it would cause a bit of stress to have one school of one type of fish constantly running into another school of different fish. It would look very much like a traffic jam, and none of us likes to be caught in one of those... ]:|

Those are just my immediate thoughts, but it occurs to me that there are very few conditions in nature where so many fish would be allowed to survive in a relatively small space. Even gentle fish will begin to "thin the heard" when there are constraints on space, which probably translates instinctively to potential constraints on resources.

Hoping that there must be a word for everything I mean...

I tend to agree with illustrae on this one. That's basically like having a sump on a saltwater tank. It wouldn't be a question of water quality... we know how dilligent you are with those water changes, and we know you provide only the best for your pandas

My fear would be that the tank would just LOOK too crowded. Now, maybe bump off one of the schools and up the numbers of the other two. E.g. 16 or so lemons and maybe 18 cardinals, plus the pandas may LOOK a bit nicer IMO.

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Back in the saddle!

What’s a cunundrum

I would say that from an abstract point of view your thought process is absolutely right; from an implementation perspective the cautions by illustrae and NowherMan6 are valid limiters.

Let’s say you wouldn’t have many schools of fish but just one large school. In this case there would be no doubt in my mind that adding 100% of water volume to the tank (indirectly) will allow you to significantly increase the size of the school.

I would not think that you could double up the numbers though, as solid waste would only collect in one of the 2 tanks.

Just my thoughts,

Ingo

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Proud Member of the New Jersey Aquatic Gardeners Club

Actually, you can and yet you cannot. There are several differencials to look at here. As with any situation, it depends on the fish, its waste production, etc etc. Now I see you are talking about FW here. But, if in a different scenario, say of SW, you would be able to double your bioload. This is done quite freqently these days. In SW, there are people that actually set up a connecting tank that is more than double or greater, to their show tank. In other words, your 4 foot tank would have a 4 ft, 8 ft, or even more feet tank, hidden in a different room with all the filters and such, as well as other stuff in it. This would increase the allowability of a higher bioload. This is also the reason that so many refugiums are built so large, as to increase the availability of the bioload increase.

For FW, if would again depend on different things. Maybe you just have one type of schooling fish in there that is at your max bioload. Then yes, I would have to say, the schoal could be doubled. Maybe you have it maxed out with an upper water schooling fish of one species. Then you add the extra tank to the mix, then yes, I would have to say you could then add a school of bottom dwellers to double the load. That is, if all filterization and such were doubled as well.

Funny thing about advanced technology. The formulas for keeping different measurements of fish, have been the same for many years, and highly accepted way back when. And in most cases, work out well. But, with the new developement of the bio-wheel, and other advanced filters, the same formulas have not changed, and in fact are reputed by many today. With this in mind, IMO, if given the proper water changes and other care, I feel that the need for the extra tank is mute. You could, for example, set up an automated drip system to continuously change the water. And have it set to keep the nitrates below a set amount. This brings into another question, of whould it work?

In other words, the biological filters would work well enough to double the fish amounts, and the water changing system, automated to keep the water changing at a speed of which the nitrates would stay below say 15ppm (for example). As the increase in bioload would increase the speed of nitrate production (given the filters are good enough to hold enough beneficial bacteria to convert all the waste as quickly as the increase load is produced), which is then detrimental to the fish, but would in turn be removed by the automated system. I feel that in the end, this amount of water changing for one tank, would be about the same as the amount changed in two connecting tanks. In other words, say that 20% in one tank is equal to 20 gals (for ease of math). Two tanks would be 40 gals. OK, so you would change this much for the bioload of the fish in just one tank (but connect to the second tank). Now, if you could just change the 40 gals out of the single tank, over a spread out period of time, such as continuously over the same week, the same amount of water is changed. I feel that the same amount of nitrates will be removed, it not more. I think it would be a better set up, as the fish would constantly be getting a fresh water source, as well, the parameters would be in check and not be fluctuating at all, like they do when we do water changes.

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There is always a bigger fish...

Hmm. some interesting notes there.

My thought wasn't doubling the fish stock necessarily, but certainly allowing an increase. An extreme example from the saltwater world is David Saxby's monster reef aquarium - which is connected to a truly gargantuan 2,400 gallon sump! And he seems to have enjoyed quite a bit of success with his setup, though the logistics involved are not for the faint hearted!

But, my thought was motivated by (among other things) the following. Assume you haven't got the space in your home for a really huge aquarium, but you can set things up so that two smaller ones (whose total volume equals that of the really huge one you actually wanted) can be connected together. Would this allow greater stocking in the 'main' aquarium compared to its nominal stocking level, and if so, what limits would be imposed?

Plus, moving away from the fishes cited above, it would provide a means of mitigating some of the management problems for certain Rift Lake keepers. Mbuna have their own well-documented woes with regard to compatibility, and one approach to try and deal with this has been the 'crowding' method - make sure that there are too many other fish to fight with as a means of keeping the internecine warfare to a minimum. Trouble is, 'crowding' per se involves water chemistry problems, particularly in an alkaline Rift Lake environment. One thought I had as an extension of the conundrum was that use of a sump/refugium could allow more Rifts to be kept together while keeping water quality at acceptable levels.

Of course, there are probably far better ways of keeping Mbuna that make all of this moot.

The thought occurred at the start of all this, that if you have limited space for a really large tank, but can keep several smaller ones, this could open up some more fishkeeping options.



Panda Catfish fan and keeper/breeder since Christmas 2002

Volume is much less important than surface area. Increase the surface area, and you will increase the loading capacity of the given volume involved.

The health of any aquarium will ultimately come down to the amount of surface area available for gas exchange. Oxygen in, CO2 out. Aerobic bacteria depend on oxygen to live, and process biological waste that is produced by fish, rotting food, rotting plants etc to complete the cycle and have a healthy aquarium.

Food for thought: A 10 gallon tank can handle a certain amount of fish with it's 200 square inches of surface area. This allows for a certain exhange of gasses, allowing for a theoritical maximum number of bacteria that can be supported. Now, think of a 100 gallon tank, but in a shape such that it's ten 10 gallons stacked on top of each other. You still have only 200 square inches of surface area for gas exchange, and still the same theoretical maxium of bacteria supported.

Now, take that same 100 gallons, but make them ten 10 gallons connected together side by side. Now you have 2000 square inches of surface area, a LOT more area available for gas exchange, and a huge increase in the theoretical maximum of bacteria that can be supported. The more bacteria that can be supported, more that is available to break down organic waste, and therefore the more life that can be supported.

You can increase the capacity of your tank by increasing surface agitation. This will increase surface area just slightly, but the circulation will bring fresh water to the bacteria, and stagnant water back up to be freshened.

So, adding another 4 foot tank will increase the capacity of the tank by double, given that you agitate/circulate the the 2nd tank like you would, or even more than the main tank, because you don't have to worry about disrupting any fish.

However, there is a point where too much is fruitless. Nitrosomonas and Nitrobacter need food to live, in the form of biological waste. You figure out a way to connect all these tanks together, and you end up with 110 gallons worth together. But your main tank is only a 55, and given space restraints, you can only squeeze in a few more, and bump the bioload to what would be similar to a 65 or 70 gallon tank. Now you've gone overboard, and this is something i threw out in the forums 3 or 4 years ago relating to the health and effectiveness of bacteria, and never really got a solid answer. I won't get into it now, but the basic jist was how healthy of a bacterical colony can you have if the food supply can only support a given amount of bacteria. The highest concentration of bacteria would generally be in the filter, as on any tank. But that's about it... if you have any other bacteria, chances are it's not around for long, and if it is it's not getting enough 'food' to be healthy.

Careful, appropriate stocking is better in this case. It's a fine balance cali, don't go nuts.

Thanks Fallout. Just want to reassure you that the question is hypothetical at this stage - I don't yet have the funds to launch into a project like this for real. But, the thought occurred that if space in a room won't allow, say, a huge 8ft long tank, but WILL allow 2 4ft ones connected, then this could solve a few problems.

In any case, a real live implementation of such a setup in my case would involve the second tank being a 24/7 vegetable refugium, and controlled waste transfers from the main aquarium to the refugium to keep the plants fed. I'd also consider the possibility of letting the Otocinclus take litle 'holidays' from the main aquarium to the refugium to snack on the algae - i think they'd like that

It also occurs to me that a FW refugium would help solve some problems with a tall main aquarium - such as the kind that would be needed to keep Angelfish or Discus happy. You could give the fishes the extra water volume (and agitated surface area) while still keeping the total setup compact enough for a living room with space restrictions. In this case, stocking would still be limited to the 'official' levels (partly because these fishes need the space regardless) but they'd get more water, and more water (especially more filtered water) is presumably a good thing for any fish.


Panda Catfish fan and keeper/breeder since Christmas 2002

Fallout is right about surface area being important, but there is a lot lacking with that theory. It does not take into acount the amount of surface agitation.

For example, lets take 5 ten gallon aquariums. One is stagnant, one has a 50 GPH powerhead, one has a 75 GPH powerhead, one with 100, and one with 125. Assuming the powerheads are placed exactly the same in the water and the power is the only variable, which has MINIMUM agitation? Which is Optimal? When is it more than enough? Can it be too much (other than being too strong for the fish to swim against it)?

Generally, stand size/shape tanks (ratio of ~2x1x1 [LxWxH]) are accepted to have enough surface area for the volume. Its generally the "designer" tanks that have these problems. But what is better: a 20XT with a lot of surface agitation or a 20L with little agitation?

ANYWAY, back on topic. Like Acidrain said, for SW, it IS worth it since SW tanks are limited more by oxygen than volume. However, in FW, it is more of volume than oxygen since the tanks usually have enough oxygen for the volume of fish you can hold.

I am in agreement with all of you. And as Racso has stated, with increase surface aggitation, as well as movement of lower levels of the water column to the upper areas, many times the surface area can be accomodated. For instance, take the 100 gal tank, that is the foot print of the 10 gal. If, there where a pump at the bottom, and it pumped the water up to a wet/dry filter that was over the tank (hidden or whatever), and the water then drained back into the tank, then it would not only be moving water from the lower (stagnent areas), but creating a massive surface area (this is the whole idea of a wet/dry) for O2 and CO2 exchange. Thus, the surface area point could be considered mute for this theory. Yes the surface area is of great importance to keeping any and all fish, but can be accomodated for.

Now Calli, you have added another factor into the mix. If you make your second tank a heavily planted tank as well, you are increasing the multiple probabilities into the mix. Now we can change the water changing schedule somewhat, as the nitrates will be kept lower by the plants, or at least the build up of them will be decreased as in a time related thing.

Thus, IMO, if a wet/dry was added to the system, you could more than double your original stocking levels. As the water would now have a nitrate exporter, thus decreasing and/or dropping the levels of nitrates. Your surface area would be greatly increased, allowing more O2 and CO2 exchange, your good bactirial growth colonies would have their growing area increased, and so on.

Your simple started theory has now become advanced and much more complicated. And I feel someone would now have to do the actual experiments to find out the specifics.

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There is always a bigger fish...

Just a thought. I'd say maybe more but not double as the beneficial bacteria would be most plentiful in the tank with the fish in it. You say it would make water changes easier, but what about your gravel vacuuming and other general maintenace? that would still be needed in the true fish tank. Also the water volume vs surface area thing...hmmm. pauses to think... I'd be afraid they'd get in the back tank, or lost en route and be darned difficult to find unless tanks were separated by a screen or something. But then you'd need to clean and maintain that too...

p.s. It would make the water more stable tho, provided adequate circulation was maintained between the two tanks

Last edited by divertran at 12-Nov-2005 07:40

In my opinion adding more water without actually adding more space for the fish to swim does not mean you should increase stocking in a tank. I don't stock my tanks based on how much bacteria it can accomadate, how good I can keep the water quality, or whether when cramped do all these fish still get along. I stock it based on the space each fish has. For my 90g my thinking was I'll start with my school of Congo tetras and they mostly hang out in 1/3rd of the tank except for select times of the day. That means if I add emperor tetras that scatter throughout the tank neither will be cramped because neither will run into each other except possibly when the male congos are displaying and spawning in the morning and evening. At that point I would have left the top levels of the tank stocked but the emperors weren't swimming in the middle at all. They scattered along the back and sides of the tank in the plants so that still left at least 1/3rd of the tank empty for majority of the day and I added the school of threadfin rainbows. The same with the bottom level. I started with my panda cory and royal pleco and went from there based on what space they used and what hiding places.

I can always increase the water quality with better filters, more water changes, and plants so water quality is never my concern. The space each fish takes and requires to live and act naturally is my concern. I would never cramp a cichlid tank because they would not act natural. It would look horrible. I don't want to just keep a bunch of pretty fish. I want to recreate a natural body of water. Although I don't really stick to one biotope because I don't like such restrictions. I did consider a sump for my 5g dwarf puffer tank or connecting it to my 90g but that's only because I hate doing water changes on small tanks. I always manage to disturb something.

Rasco -

You can increase the capacity of your tank by increasing surface agitation. This will increase surface area just slightly, but the circulation will bring fresh water to the bacteria, and stagnant water back up to be freshened.