How do you accurately predict/measure water flow?

[Iamgarrett]

I'm in the planning stages for my tank, and wondering how the heck to accurately and best set-up a pump and know where your high/medium/low movement areas are.

This is so basic of a question I guess that my searches have failed me.

 

[Ron Reefman]

Hi Garrett and welcome to the forum.

The overall flow in your tank is measured by how often the water in your tank is moved or turned over and is listed as turns per hour.

Example: Lets say you have a 100g tank (the size of your sump does NOT figure in). You use a 1000gph return pump from your sump. 1000gph divided by 100g tank equals 10 turns per hour. That's too low (maybe ok for fish only).

So you add 2 powerhead that run at 500gph. So 1000gph (return pump) + 500gph (powerhead) + 500gph (powerhead) = 2000gph divided by the 100 gallon tank is 20 turns per hour. That's good for fish only and soft corals.

The numbers only go up from there. How you calculate in a wave maker pump is up to you. I usually take the ave gph (between the low of zero and a high of ???gph). Some sps tanks can run as high as 60 to 80 turns per hour.

 

[Timfish]

No good way to actually check the flow in various places in your tank. Ron Reefman explained the best way to get a general idea of flow. I have to disagree with needing such high flow rates though. Some of my acros I've gotten from friends who keep high flow rates had no problems adjusting to little or no flow. And one of the surprises scientists found looking at the few reefs not heavily impacted by us was Nikko reef in Palau that's pretty much stagnant but is one of the most pristine in the world. And if you want to dig into the minutiae of the science the surface boundary layer around corals is only a couple millimeters thick but it allows corals to manipulate parameters at their surface and higher flow rates make it harder for them to do.

 

[rjjr1963]

I just started dosing Coral Snow which is a white chalky kind of liquid. It makes the tank cloudy so when you first put it in you can kind of see how the flows goes around in the tank. You could also tie little pieces of thin plastic to a small rock and place it at various spots around the tank to see what kind of flow you have in each area.

 

[Ron Reefman]

No good way to actually check the flow in various places in your tank. Ron Reefman explained the best way to get a general idea of flow. I have to disagree with needing such high flow rates though. Some of my acros I've gotten from friends who keep high flow rates had no problems adjusting to little or no flow. And one of the surprises scientists found looking at the few reefs not heavily impacted by us was Nikko reef in Palau that's pretty much stagnant but is one of the most pristine in the world. And if you want to dig into the minutiae of the science the surface boundary layer around corals is only a couple millimeters thick but it allows corals to manipulate parameters at their surface and higher flow rates make it harder for them to do.

Just a point of info, I didn't mean to imply that high flow rates are required, just that there are reefers who have sps tanks and swear by their high flow rates. But as far as I'm concerned, everybody's tank is different... just like most reefs are different.

 

[Iamgarrett]

Thanks for the replies. Maybe when I first set everything up I'll stir some sand? Just hoping I can minimize repositioning corals as much as possible (once I get to that point).

And the explanation about turns was very helpful.


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[Sk8r]

Your pump will have a gph rating (gallons per hour)---mine for a 105 gallon has a 2350 gph rating. But there is also 'head' (lifting) which cuts into the gph. My sump is in the basement, my tank 13 feet overhead. So I have an additional pump, a Gyre, which provides a rolling, horizontal flow.
When I had a 52 gallon, I used a 950 gph pump and that was all I needed, but I used two SeaSwirls for the outlets, which sent that 950 as a horizontal flow.

If you have a high flow tank, I advise against superfine sand, or it will walk, constantly, and kill corals; medium grain aragonite stays put, well, except for fish moving it.