THere's not only 'how much' but what kind.
Flow from a pump is measured in gph, gallons per hour. Height to which a pump lifts a fluid, say from your under-stand sump to the top of the tank, is called head.
Head reduces gph. So if you ask a pump with 500 gph to pump something to the second floor of your house, the column may reach max height in the hose and stall there, never reaching the tank.
Valving back a strong pump to reduce its gph is like asking it to pump to a longer hose uphill. IE, it's nothing but head pressure, and the pump won't die of it. They're designed to work under those conditions. It is better to get a slightly stronger pump than you may need and valve it down than to get a weaker pump struggling to do what you need.
It is ok to put a valve in the UP line. Never, ever, ever,ever put a valve of any kind in the drain line. If the drain line clogs you'll need a new carpet.
How much flow? Depends on what you keep. With lps corals and a deep tank, I'm running (with about 15-20 feet of hose between floors) a 2350 gph pump and supplementing it with a Maxspect gyre (to send flow sideways and make it roll UNDER the rock structures) at 75 % in a 100 gallon tank.
In a 50, with an under-stand sump, I used a pump with 950 gph and two Sea Swirls, which nod back and forth as they serve as nozzles for the return pump flow, aimed at each other, which produces turbulence.
Turbulence is a good thing. Chaotic flow can be made to bounce off walls (the Gyre does this) or two powerheads aimed at each other can produce turbulence.
All this really helps aeration. The top of the water should be rippling and roiling. Likewise the fall into the sump aerates; and so does your skimmer. This is a big plus for everything you keep.
Corals with soft tissue don't like to be battered by a water stream. Nothing much enjoys a fire hose attack. The currents in your tank help provide exercise and variety for your fish---sort of like invisible furniture in a room---but they shouldn't struggle, either.
Fine sand tends to 'walk' in strong flow. Personally, I tried it, and after losing a couple hundred dollars worth of corals to it, and facing the choice of taming the flow or changing the sand---I changed the sand. Everybody was happier with the coarser sand.
Main thing, buy a little stronger than you need; never valve a drain line; and observe how your corals and fish react; you can valve down a too-strong pump to accommodate them, or redirect a powerhead. Food should generally distribute itself and not whisk away to oblivion in the downflow. Move outflow, try for some turbulence, and don't blast any coral or nem with a direct hard stream.
Flow from a pump is measured in gph, gallons per hour. Height to which a pump lifts a fluid, say from your under-stand sump to the top of the tank, is called head.
Head reduces gph. So if you ask a pump with 500 gph to pump something to the second floor of your house, the column may reach max height in the hose and stall there, never reaching the tank.
Valving back a strong pump to reduce its gph is like asking it to pump to a longer hose uphill. IE, it's nothing but head pressure, and the pump won't die of it. They're designed to work under those conditions. It is better to get a slightly stronger pump than you may need and valve it down than to get a weaker pump struggling to do what you need.
It is ok to put a valve in the UP line. Never, ever, ever,ever put a valve of any kind in the drain line. If the drain line clogs you'll need a new carpet.
How much flow? Depends on what you keep. With lps corals and a deep tank, I'm running (with about 15-20 feet of hose between floors) a 2350 gph pump and supplementing it with a Maxspect gyre (to send flow sideways and make it roll UNDER the rock structures) at 75 % in a 100 gallon tank.
In a 50, with an under-stand sump, I used a pump with 950 gph and two Sea Swirls, which nod back and forth as they serve as nozzles for the return pump flow, aimed at each other, which produces turbulence.
Turbulence is a good thing. Chaotic flow can be made to bounce off walls (the Gyre does this) or two powerheads aimed at each other can produce turbulence.
All this really helps aeration. The top of the water should be rippling and roiling. Likewise the fall into the sump aerates; and so does your skimmer. This is a big plus for everything you keep.
Corals with soft tissue don't like to be battered by a water stream. Nothing much enjoys a fire hose attack. The currents in your tank help provide exercise and variety for your fish---sort of like invisible furniture in a room---but they shouldn't struggle, either.
Fine sand tends to 'walk' in strong flow. Personally, I tried it, and after losing a couple hundred dollars worth of corals to it, and facing the choice of taming the flow or changing the sand---I changed the sand. Everybody was happier with the coarser sand.
Main thing, buy a little stronger than you need; never valve a drain line; and observe how your corals and fish react; you can valve down a too-strong pump to accommodate them, or redirect a powerhead. Food should generally distribute itself and not whisk away to oblivion in the downflow. Move outflow, try for some turbulence, and don't blast any coral or nem with a direct hard stream.
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