More filtration = more fish?

[Essjay]

I have read elsewhere that increasing filtration means that more fish can be kept in the tank, but I am having a hard time believing this.

For example, take a 50 gallon tank.
The argument is that this tank can hold a certain amount of fish if it has an internal/HOB rated for 50 gallons. Change the filter to an internal/HOB rated for 100 gallons, and you can add more fish. Then change the internal/HOB for an external (cannister) filter rated for 50 gallons, and the amount of fish the tank can hold increases again. Finally, change the external for one rated at 100 gallons, and the tank can hold even more fish - almost double the amount it could hold with a 50 gallon internal/HOB.

To my mind this is wrong. There is a lot more to stocking a tank that the size and type of filter.

Am I right? Or does over filtering a tank really mean that it can hold more fish?


Discuss .......

 

[seangee]

Only up to a point if you are heavily stocked and not planted. I deliberately over filter my Koi pond because plants don't last long in there.

The trade off that too many people miss is more fish means more waste, nitrates, hormones and pheromones so more water changes are required, even if the filter(s) are "coping" . Adding filtration will deal with the additional ammonia and nitrites but won't lead to healthier fish. Without the water changes they will probably grow more slowly and have a shorter life.

If you do want to overstock heavily planted is probably the better option because at least that will help keep the nitrates in check.

 

[Essjay]

The people who say that increasing filtration means more fish never mention plants, or water changes. The impression I get is that they think that all you have to do is get a bigger filter, get more fish and carry on with the same maintenance regime as the filter will take care of everything.

It was your 'two cans' thread that prompted me to ask this question To my mind, all increasing the size or type of filter does is increase the amount of water per hour that passes though the filter, and does not affect the stocking level.

 

[DrRob]

I'm a serial filter oversizer. I also tend to run low stocking densities. For me it's all about best possible conditions and the greatest chance to compensate for changes in the environment.

In theory, you could overstock a tank and keep the water parameters right with an oversized filter and lots of water changes, but you'd still have issues with territory, which I often find are the biggest issues for happy fish.

 

[Colin_T]

It's all been covered above but going back 100years ago fish tanks did not have filters, heaters or good lights. Tanks were kept planted and people often had gas lamps or low wattage incandescent light globes near the tank to increase lighting. And they either heated the room the tank was in, or used a candle, gas or oil lamp under the tank to keep the water warm. There were metal double tier stands with adjustable shelves underneath the top shelf. The fish bowl/ tank sat on the top shelf and you had candles or lamps on the shelf underneath the tank.

Skip forward to the 1950s? and airpumps and fluorescent lighting became available and made a huge difference. Air operated filters were developed and all of a sudden you could keep a lot more fish in the tank.

Power filters started to become available in the 70s and filtered the water much quicker than air operated filters and that helped people keeping marine aquariums. And by the 80s there were good lights, filters, heaters and pumps and fish keeping became a lot easier.

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Filters allow you to keep more fish in a smaller volume of water, and larger filters can allow you to keep higher stocking levels compared to aquariums with smaller filters. However, de-nitrators, protein removers and or water changes, are eventually needed to keep nitrate levels low enough so the fish are not adversely affected.

Even tho bigger filters do hold more beneficial bacteria and turn the water over faster, higher stocking levels increase the risk of disease outbreaks and if the filter fails, the water quality deteriorates much faster and usually causes the loss of all livestock in the tank.

Good filtration is essential in helping keep water cleaner for longer, and allowing more fish to live in the aquarium. However, feeding, healthy growing aquatic plants, and water changes are also important for the long term health of the tank inhabitants.

 

[AbbeysDad]

The notion that increased filtration by itself will support more stock is essentially incorrect. Filters are a nice platform for beneficial bacteria because in theory, food and O2 are delivered regularly. But filters can also become nitrate factories. As Byron pointed out in the previous 'two can' thread, water may appear cleaner with more filtration, but it rarely is. Fish, fish food, and any additives create pollution. Some pollution is removed by fast growing plants, some by bacteria, but some remains and builds up regardless of the filter(s) being used. At the same time, necessary minerals like calcium and magnesium are being used up by fish and plants. The only logical solution is pollution dilution with routine periodic partial water changes.
So, setting aside potential overcrowding, territorial and stress matters, one could conclude to a point that with increased volume/frequency of partial water changes (perhaps along with fast growing plants), more stock could live comfortably in a given tank.
But 'pushing' this is akin to less frequent/volume water changes and/or poor tank/filter maintenance and as @Collin_T suggested, the time until potential disaster gets shorter.

 

[Chief Brody]

I've heard the word "unnatural" come up in a similar conversation. This was also coming from someone who keeps tropical fish in ponds outside and catches them every year and so on... he insists... his fish are beautiful, but should there really be that many fish in one place ever? Where does our responsibility to both maintain a healthy specimen and potentially an entire bloodline for the future benefit of the species? I think realistically we're at a point where certain fish may only be able to thrive in captivity and so we should accommodate. I personally feel if I can get every fish in the tank somewhat comfortable it's doable. Filtration is an afterthought. We can always build a huge filter. What about the ethics involved around keeping fish in less than ideal conditions with a volume of fish they would never really encounter in the wild. I'm thinking mainly of cichlids here not necessarily the big pelagic species. Territorial species tend to have large swathes of real estate to themselves.

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[Chief Brody]

.... at the same time there's only so many tanks available in the world and these fish need homes! So part of me feels like keeping as many as possible at all times is important as well. I guess it's a mighty balance we all strive for. Pushing the sytems to the max without crashing all the while not stressing the animals. Knowing the behavior of the individuals is key for any of it to work. Even small fish can be brutal. There's always gonna be a runt or bottom of the pecking order. It's raw in there... but I know there's worse outcomes for a fish in the trade than ending up with me so I tend to back 'em in
Out of kindness I suppose

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[seangee]

It was your 'two cans' thread that prompted me to ask this question

In fairness the two cans tank was never about pushing anything. I downsized from a 350l to an Aquavogue 185. This shipped with a perfectly good filter (Ocellaris 850) but I was in a hurry as the main reason for the change was house decoration / renovation and moving the old tank was beyond me (and the stand was on its last legs after 15 years). So once I had found homes for the fish I couldn't keep I bought new hoses for the new tank and simply moved all the fish and the Fluval 406 across on the same day.

A year later I was clearing out my study and on the verge of chucking out the Aqua One filter which was untouched in its box. It wasn't worth enough for me to justify flogging on eBay. But the 406 is pretty long in the tooth and I decided that I'd feel a bit silly if I'd thown out a perfectly good filter and it failed within a few months. So I set it up and plugged it in. Now I have peace of mind and don't have to worry about storage space for a spare.

 

[Essjay]

It was the other comments about too much water flow etc that made me wonder about stocking. Personally I don't think having a filter rated for a bigger tank affects the stocking level very much as fish excrete so many things that are not removed by the filter. Water changes are the only way to remove these, though having lots of live plants will help. I have tried explaining this to someone who was convinced that more filtration means a lot more fish but I don't think I made a good job of it.

 

[seangee]

Interesting the AqAdvisor calculator does not change its stocking level whether I declare one (either) or both of these filters. Any way I list them it regards my tank as being at 80% and shows the percentage over filtered. If I remove both and add a smaller filter it shows the same but warns that I need to add filtration. I am comfortable with my stock level and won't be increasing it.

Lets NOT debate the pros and cons of such calculators )) but in this instance it may help convince your friend by presenting "scientific" evidence that the tank has a fixed capacity based on size / volume alone.

 

[Fishmanic]

quote from Seangee
Lets NOT debate the pros and cons of such calculators )) but in this instance it may help convince your friend by presenting "scientific" evidence that the tank has a fixed capacity based on size / volume alone.


That is very true...size of tank limits amount and size of fish you could house even if overfltered.

I always run two filters on each of my 3 moderately planted tanks. One is a hang-on-back filter that is oversized for the tank...and the other is a sponge filter. For instance in my 35 gallon tall hex, I run an aquaclear HOB cable of filtering 50 gallons and a reticulated sponge filter capable of filtering 40 gallons. Sometimes if there is a power failure, when the electricity comes back on, the HOB wont auto-prime and thus will stop working. I have peace of mind knowing the sponge filter will prevent rising ammonia and and nitrite levels till I realize the HOB filter is not working properly.

Another benefit of two filters in each tank, is if I have to set up a hospital tank or a quarantine tank, I can use one of the sponge filters from a healthy tank to instantly cycle it.

 

[NickAu]

When dealing with canister filters its about how they are set up whats in them, It can also be about water capacity and that can be very important when running a small tank.

Laugh all you want that canister filter holds 6 liters of water. All it ever had in it was some filter floss.

 

[Essjay]

That cannister just about doubles the volume of water flowing through the tank. In this case, maybe the tank can hold more fish that a 6 litre with a small internal rated for 6 litres

 

[AbbeysDad]

"That is very true...size of tank limits amount and size of fish you could house even if overfltered."

I think it's important to realize that filters (overfiltering or not) merely address the appearance (or clarity) of the water. Filters, unless loaded with various chemical media, do not remove pollutants or improve water chemistry/quality.