# Question to Sump Experts - Drain line size, return pump size



## Captured Moments (Apr 22, 2010)

Trying to figure out flows in sump design. For example for a 210 gallon tank, what size return pump should you aim for? How many gallons of water should the pump cycle in the sump per hour? taking into consideration the head pressure. Assume a 90-100 gallon sump tank size. Then we need to make sure the drain line(s), maybe 2, can safely handle the overflow volume dictated by the return volume of the sump pump, correct? Is there a formula to figure out the safe diameter of a drain pipe on overflow given a known flow rate in gallons per hour? You wouldn't want a drain too small or what if it clogs then wet floor?


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## fkshiu (Apr 22, 2010)

A rough and imprecise rule of thumb is a return pump flow rate of 3 - 5 times total system volume. Therefore, a 300-gallon system your looking at a flow rate (after head loss) of anywhere from 900 to 1,500 gph.

I actually find this rule of thumb be a bit of overkill. You simply need enough turnover to sufficiently draw enough display tank water over your heaters, bio-filter and other equipment in the sump to maintain stable parameters throughout the system. My 160-gallon reef system only has about a 350 gph turnover and its been running fine for years.

Too powerful a return pump can cause noise, heat and micro-bubble problems not to mention being a waste of electricity. Furthermore, too much flow can reduce the effectiveness of UV filters, protein skimmer and other chemical media because of the reduced dwell time.

The question of flow within the display tank is a separate issue depending on what you are keeping. Nowadays, very few people rely solely on their return pump to provide flow. It is actually more efficient to use propellor-driven powerheads such as korallias for such flow.

As far as drain size is concerned, here's the calculator I use:

Drain/Overflow Size


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## Captured Moments (Apr 22, 2010)

That's good information. The flow rate through the sump is actually lower than I thought and I am understanding now that a lower rate of flow would provide the advantages mentioned.


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## SeaHorse_Fanatic (Apr 22, 2010)

Are you building a fw or sw sump?

Slow is good for sw so the protein skimmer has more time to clean the water.

Fast is good for fw because the filter materials can mechanically remove more crap.


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## Captured Moments (Apr 22, 2010)

It's for freshwater sump. I was wondering how much flow should be the minimum and the max circulating through the sump.


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## SeaHorse_Fanatic (Apr 22, 2010)

As I mentioned, with a fw sump, a high flow rate is good because the water passes through the filter media more times per hour. 

Rather than focus on just gallons/hour, other questions to consider are:

what size pump & amount of electricity it will use (for instance, large Mag pumps produce a lot of heat which may be an issue in the summer).

Internal or external pump - Internal's advantage is that if it leaks, the water is contained in the sump. External's advantage is that it does not really contribute to the heat issue.

Sump design - make sure filter pads & media are easily accessed so that maintenance is easy.

Do NOT go to maximum flowrate on your downpipes - Otherwise if it clogs a bit, you risk problems.

I would probably calculate how much flow your downpipes can handle and figure on going at say 80% of max. capacity to give you some wiggle room. 

If the sump/overflow system can handle it, even 1500 gph would not be too much IMO, bu the critical questions for me are whether the plumbing can handle that much flow and will your fish like that much water movement.

BTW, you can T or branch off the returns to provide 4 or more return outlets.


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