GPH hazards to fish

[eon aquatics]

How much GPH/flow rate is too much for fish?
Does it matter as long as the output valve is under the gravel or some heavy larger rocks to disperse the flow rate so the fish dont become bothered?

 

[Milingu]

It totally depends on which fish is in your tank Most fish can't get enough flow in the aquarium. But there are some exceptions like for example bettas or some guramis that don't like flow at all.

 

[Guppy_R]

Flow in a tank/pond isn't compulsory right, even if there are species who live in areas with a lot of flow naturally

 

[Redshark1]

For my Clown Loaches in MY TANK I experimented and found that if the flow was more than 10 x turnover (i.e. if the total tank volume was filtered more than ten times in an hour), my Clown Loaches stayed in their retreats and didn't come out much. Below this they came out much more. I was able to observe that they could sit on the gravel and chill without having to fight the current.

 

[duanes]

It totally depends on which fish is in your tank Most fish can't get enough flow in the aquarium. But there are some exceptions like for example bettas or some guramis that don't like flow at all.

I agree, some species do best with lots of flow.
More flow usually indicates a higher dissolved oxygen content some species need.
It even tempers aggression in some riverine cichlid species, like Geophagus, Rheoheros, Chuco, and Tomocichla that come from riffles and rapids.
Of course you wouldn't provide extra flow for placid water species, like some Bettas, discus, or gouramis.
Below is a video of the flow I use in my 180 gal tank for riverine cichlids and tetras, the main pump throws 1500GPH at 4 ft of head.
Flow

 

[Lepisosteus]

My reef tank was pushing 75x turnover within the tank. My planted tank maybe 3

 

[duanes]

The same as for fish, plants differ in their needs for flow.
For some plants a heavy flow is perfect.
I find Vallisneria and crypts do well in strong flow tanks.

In one of my planted sumps, I tried too much flow, and my lilies melted away, so I reaimed flow ports, and relocated some sunken logs to create a low flow corner, now the lilies are returning to health..

 

[TwoHedWlf]

How much GPH/flow rate is too much for fish?
Does it matter as long as the output valve is under the gravel or some heavy larger rocks to disperse the flow rate so the fish dont become bothered?

Except for right around the outlet of the pump you'll probably start getting a bit much for slow water fish once you hit around 50X turnover per hour. Something like Angels, discus, fancy goldfish might not be able to manage.

Most cichlids and faster fish won't have a problem up past 100X, especially with some calm spots when they want to take a break.