What Exactly Is Flow

[MarkGabb]

ok im sure this has probably been answered but i cant seem to find a strait easy to understand version of it...
 
what exactly is flow?
and what does it matter?

 

[fluttermoth]

Flow is, quite simply, the amount of water movement in the tank. Obviously, all tanks need a certain amount of flow; both to keep the water moving through the filter and to allow gaseous exchange at the surface.
 
Different fish need/prefer different amounts of flow. Of course, you should check the individual requirements of fish species before you buy them but, in general, fish with long flowing fins (guppies, Siamese fighters) or tall bodies (angels, discus) come from areas that have fairly slow moving water, while fish that have horizontal stripes and slim, torpedo shaped bodies (zebra danios, torpedo barbs) will have evolved in fast moving water.
 
Some fish (hillstream loaches, many 'plecs'), are so adapted to very fast moving waters (that are often cooler than standard tropical temperatures, and contain a lot more dissolved oxygen) that they will do very poorly in standard set ups.

 

[DrRob]

It's also seen referenced in planted tank discussions, referring partly to what Flutter says above, but also taking into account the flow around individual parts of the tank, rather than the total movement of water, so lots of flow with dead spots would be worse than a lesser flow with a better spread. It becomes complicated with hardscapes blocking flow, but also with growing plant masses clogging things up as well.

 

[MarkGabb]

Awesome. Thanks for the answers guys

 

[delkimgreen1]

I would say i have a lot of flow in my tank and a lot of surface movement also, are there any fish you wouldn,t put in, this weekend im going to buy 6 rainbows ?

 

[Byron]

I would say i have a lot of flow in my tank and a lot of surface movement also, are there any fish you wouldn,t put in, this weekend im going to buy 6 rainbows ?

 
Which species of rainbow fish are you considering?  The habitat of a species is a good clue to the water flow requirements.  Generally speaking, fish should not be maintained permanently in fast water currents, unless of course they are designed for this.  A fish has to work much harder in a current, so this aqffects the fish's physiology and can cause stress and resulting health problems and premature demise.
 
It would also help to know the "flow" you have.  Excessive flow is detrimental to many fish, and to plants.  Everything is relative.  Rainbowfish require good clean and stable water, but strong current is not indicative of better water quality.  After all, it is possible to have a very healthy aquarium with no filter at all; I've done it.
 
Byron.

 

[delkimgreen1]

well how do you actually measure the flow though?  i have a 10 inch inlet bar with about 10 holes in it pumping in the water from the pump and the air bubbler set quite high which rips the surface area of the tank to cause disturbance and all in all its a fast amount of movement. That said there are enough slack spots for the fish as well. 

 

[Byron]

well how do you actually measure the flow though?  i have a 10 inch inlet bar with about 10 holes in it pumping in the water from the pump and the air bubbler set quite high which rips the surface area of the tank to cause disturbance and all in all its a fast amount of movement. That said there are enough slack spots for the fish as well. 

 
I go by what I see in the tank.  All my tanks are planted, and I do not see plants swaying in the current, except for those right under the filter return (spraybar or spigot).  There is some surface movement at this area as well.  In two tanks I have a bit more current at the filter return end, solely because of the fish species.
 
I've never fussed over turn-over rates and all that; I use a canister filter designed for the tank size, adjusting the flow according to the fish requirements by using the spray bar aimed into the wall or whatever.
 
Byron.

 

[delkimgreen1]

Ok thanks for that but my bar is facing into the tank not against the back wall so is that acceptable or is it better facing the wall ?

 

[delkimgreen1]

while we are on the subject of spray bars/pump bars where can you get the little sucker clips as mine are perished and im having real trouble keeping the pipe in the right position.

 

[Byron]

Ok thanks for that but my bar is facing into the tank not against the back wall so is that acceptable or is it better facing the wall ?

 
This depends upon the fish's needs.  In another thread I believe you mentioned Boesemani rainbows (species Melanotaenia boesemani).  This fish occurs in the Ajamaru Lakes region of Indonesia, and is found in the lakes in the shallow areas with dense vegetation and in some of the surrounding tributary streams.  This suggests fairly slow water movement.  Add to this the need for very clean and stable water for all species in this group, you would want what I may call moderate filtration.  A canister for example, rated to the tank volume, with the spray bar aimed into the glass wall so the current hits the wall and falls mainly down and across the tank.
 
If I've mixed up the species, correct me, and I will adjust my suggestion if appropriate.  BTW, this species is reported not to do well in soft acidic water.  The lakes of its habitat have hard water with a pH between 8 and 9, which is certainly high, comparable to the African rift lakes.  Interestingly, the tributary streams in which this fish is sometimes seen is much the opposite, having soft water with a pH between 6 and 6.5, but it is quite possible that the fish do not remain permanently in these streams but migrate into the lakes.  Anyway, a good fish species for those with moderately hard tap water, which is fairly common.
 
Byron.

while we are on the subject of spray bars/pump bars where can you get the little sucker clips as mine are perished and im having real trouble keeping the pipe in the right position.

 
There are packages of these available, probably in some fish stores, and certainly online.  I buy them every so often for heaters and filter tubes, as they do wear out as you say.  They come in various sizes and types, so look for the ones like you have.

 

[delkimgreen1]

Thanks again Byron, yes i have just bought some boesami rainbows (6) and they seem ok at the moment. My ph is a stable 7.4 !!

 

[Byron]

Thanks again Byron, yes i have just bought some boesami rainbows (6) and they seem ok at the moment. My ph is a stable 7.4 !!

 
That's fine.  In my experience, it is not so much the degree of pH, but whether it is acidic or basic, generally speaking.  There are as always exceptions of course.