What Classifies As A 'strong' Current?

[ZoddyZod]

I've got a Fluval U3 in a 125l tank which appear to create quite a good circulating current. I'm doing plenty of research to find fish that are suitable for the tank and one grey area is the speed of the current. Several fish that I am interested in dont appear to like a 'strong' current, so my question is.......what is a 'strong' current, and how would I go about understanding if mine is soft/medium/strong etc?

 

[sjolliff]

I've got a Fluval U3 in a 125l tank which appear to create quite a good circulating current. I'm doing plenty of research to find fish that are suitable for the tank and one grey area is the speed of the current. Several fish that I am interested in dont appear to like a 'strong' current, so my question is.......what is a 'strong' current, and how would I go about understanding if mine is soft/medium/strong etc?

i had a U3 and just changed over to the 205

on the U3 depends on which setting, does put a decent current out

not as much as a 4500 powerhead like,

i had my U3 on the 1st setting the top outlet and i would say its a soft current

 

[waterdrop]

How to rate and adjust water currents?

Heck if I know! Good question! I've just come to feel this is one of the many areas of the hobby where "knowing" is less based on objective or measured information but more on trial and error, personal judgement and experience. I -have- come to feel there's more to it than I first felt when I returned to the hobby to become a "Re-Beginner."

The major subtopics I can think of are:
1) surface movement (especially relating to oxygen gain and CO2 loss.)
2) Overall flow rate from filters.
3) Added flow rate from any powerheads you have in addition to filters (if you have any.)
4) water movement down near the bottom, farther away from your filter output
5) circulation pattern

Major tank issues related to the topic are:
1) Oxygen for fish.
2) CO2 for plants.
3) Effectiveness of debris removal by the filters.
4) Algae.

Perhaps some of our members more experienced than me can "have a go" at that skeleton and make it different/better or more commented on.

~~waterdrop~~

 

[nmonks]

Current is best determined objectively, by comparing the turnover of your filter against the size of your tank.

A "gentle" current is anything up to about 4 times the volume of the tank per hour. So for a 125-litre aquarium, that would be up to 4 x 125 = 500 litres/hour. This is an adequate current for small fish, things like neons, as well as those species that don't like strong currents, such as bettas, angels and some of the labyrinth fish.

A "medium" current is between 4 to 6 times the volume of the tank per hour; for 125-litre aquarium that would be up to 6 x 125 = 750 litres/hour. This is adequate for big fish that create a lot of mess, or river-dwelling fish that need a bit of current to swim into; things like barbs, danios, most cichlids, Corydoras catfish, etc.

A "strong" current is around 8 to 10 times the volume of the tank; for the 125-litre aquarium this is up to 1250 litres/hour. At the lower end this is what you'd choose for big, very messy fish like oscars and plecs, and at the higher end the sort of current needed by loaches, hillstream fish, Tanganyikan cichlids, and so on. It's also comparable to turnover rates in marine aquaria.

Cheers, Neale

I've got a Fluval U3 in a 125l tank which appear to create quite a good circulating current. I'm doing plenty of research to find fish that are suitable for the tank and one grey area is the speed of the current. Several fish that I am interested in dont appear to like a 'strong' current, so my question is.......what is a 'strong' current, and how would I go about understanding if mine is soft/medium/strong etc?

 

[ZoddyZod]

Current is best determined objectively, by comparing the turnover of your filter against the size of your tank.

A "gentle" current is anything up to about 4 times the volume of the tank per hour. So for a 125-litre aquarium, that would be up to 4 x 125 = 500 litres/hour. This is an adequate current for small fish, things like neons, as well as those species that don't like strong currents, such as bettas, angels and some of the labyrinth fish.

A "medium" current is between 4 to 6 times the volume of the tank per hour; for 125-litre aquarium that would be up to 6 x 125 = 750 litres/hour. This is adequate for big fish that create a lot of mess, or river-dwelling fish that need a bit of current to swim into; things like barbs, danios, most cichlids, Corydoras catfish, etc.

A "strong" current is around 8 to 10 times the volume of the tank; for the 125-litre aquarium this is up to 1250 litres/hour. At the lower end this is what you'd choose for big, very messy fish like oscars and plecs, and at the higher end the sort of current needed by loaches, hillstream fish, Tanganyikan cichlids, and so on. It's also comparable to turnover rates in marine aquaria.

Cheers, Neale

Thanks for the detailed response. That is as clear an answer as I could've hoped for. The U3 turns over 600L per hour so I'm in the "medium" bracket.

 

[ZoddyZod]

How to rate and adjust water currents?

Heck if I know! Good question! I've just come to feel this is one of the many areas of the hobby where "knowing" is less based on objective or measured information but more on trial and error, personal judgement and experience. I -have- come to feel there's more to it than I first felt when I returned to the hobby to become a "Re-Beginner."


~~waterdrop~~

The more I dig into this hobby the more of these areas I seem to find and the more it stimulates my interest.

I do feel mildly terrified by the 'trial and error' aspect to it all, simply because I would hate any negligence on my part to hurt/kill any of the fish I keep.

 

[waterdrop]

Well, I think its a good thing Neale brought me back to earth with some straightforward turnover summaries. Thanks Neale, advice taken.

~~waterdrop~~

 

[nmonks]

Not sure it's about coming "back down to earth" but glad to have helped. In any case, the factors waterdeep mentioned are perfectly viable and indeed important ones to consider.

For example, if you have a big fish that doesn't like strong current, like discus, how to you reconcile the medium-high turnover needed for clean water against the slow water current typical of its habitat in the wild? In this case, you'd look at the type of filter being used, and also at the type of filter outlet used as well. A canister filter equipped with a long spray bar is producing a less turbulent flow of water than one equipped with just a plain spout or a venturi jet return. So one way to make high water turnover rates less turbulent (and so less stressful on fish from slow water habitats) is to add a spray bar, or to point the return towards the glass or a big rock, so that the current is spread out.

It's also worth mentioning that turnover rates drop dramatically over time. When you set up a filter from new, it'll seem to have a very strong current, but as the weeks pass you'll see flow rates dropping as the mechanical filter medium becomes blocked with detritus and silt. One reason you choose high turnover rates for messy fish is precisely this: it provides for sufficient turnover rate for biological filtration even when the filter is partially clogged. At a guess, I'd say my canister filters drop in turnover rate by around 50% within 4 weeks.

The importance of turnover for oxygenation is often overlooked. It's circulation of the bottom layer of water up to the top that matters, not bubbles or splashing. This is why subtropical and tropical loaches need to be kept in tanks with good rates of turnover: it's not that they have unusually high oxygen demands compared to other fish, but that they won't tolerate low levels of oxygen at the bottom of the tank where they live. By contrast, things like plecs and Corydoras are air-breathing fish that can, to some extent, avoid problems by gulping air from the top of the tank should they need to.

Cheers, Neale

Well, I think its a good thing Neale brought me back to earth with some straightforward turnover summaries. Thanks Neale, advice taken.

 

[Tropical_Fish]

I've been wondering a little on this myself,

I've setup a fluval 304 on a 70 Litre tank - that gives 1000 litres per hour, so about 14x turnover.

I've played around with the output (partly due to making my own output pipe) and I can make quite a strong current in the water, or I can turn the output round so it points at the glass - this creates a very high current in a small area of the tank but the rest of the tank has a very gentle current. As long as the fish are smart enough not to go in the strong bit then they would be fine.

 

[waterdrop]

Not sure it's about coming "back down to earth" but glad to have helped. In any case, the factors waterdeep mentioned are perfectly viable and indeed important ones to consider.

For example, if you have a big fish that doesn't like strong current, like discus, how to you reconcile the medium-high turnover needed for clean water against the slow water current typical of its habitat in the wild? In this case, you'd look at the type of filter being used, and also at the type of filter outlet used as well. A canister filter equipped with a long spray bar is producing a less turbulent flow of water than one equipped with just a plain spout or a venturi jet return. So one way to make high water turnover rates less turbulent (and so less stressful on fish from slow water habitats) is to add a spray bar, or to point the return towards the glass or a big rock, so that the current is spread out.

It's also worth mentioning that turnover rates drop dramatically over time. When you set up a filter from new, it'll seem to have a very strong current, but as the weeks pass you'll see flow rates dropping as the mechanical filter medium becomes blocked with detritus and silt. One reason you choose high turnover rates for messy fish is precisely this: it provides for sufficient turnover rate for biological filtration even when the filter is partially clogged. At a guess, I'd say my canister filters drop in turnover rate by around 50% within 4 weeks.

The importance of turnover for oxygenation is often overlooked. It's circulation of the bottom layer of water up to the top that matters, not bubbles or splashing. This is why subtropical and tropical loaches need to be kept in tanks with good rates of turnover: it's not that they have unusually high oxygen demands compared to other fish, but that they won't tolerate low levels of oxygen at the bottom of the tank where they live. By contrast, things like plecs and Corydoras are air-breathing fish that can, to some extent, avoid problems by gulping air from the top of the tank should they need to.

Cheers, Neale

Well, I think its a good thing Neale brought me back to earth with some straightforward turnover summaries. Thanks Neale, advice taken.

Yes, I remember thinking quite a bit more about stratification back in the days of little bubble box filters in the 50's etc. Your point about filter flow rate following a regular rhythm of slowly clogging and then being cleaned is well taken and I'll hope to remember this point more often when discussing with beginners here in the future. I do still sincerely feel some of the grid of things you and I have mentioned about the general topic of circulation show that its a good example of one of these areas of the hobby where there are difficult things to understand and where discussion/ideas/new-things that might push the hobby farther than its been don't seem to happen too often.

~~waterdrop~~
ps. Have wondered if you might know a friend of mine, fellow named Peter Bradley who writes on plants and other topics sometimes over there?