How slow is too slow through sump?

[M_Jaco]

And to touch on the thought of detritus settling in the tank and not making it to the sump...

with sufficient flow in the display tank, one can assume a "completely mixed flow reactor" exists in the display, keeping solids in suspension until they are removed via the overflow. If nothing settles in the display tank (besides the unavoidable percentage that gets trapped in rock crevices), it'll eventually make it down the drain.

 

[KafudaFish]

Fast enough to not see the surface scum and slow enough not to hear the return pump.

 

[DaveMorris]

I'm always amused by the idea of matching sump flow to skimmer flow. Unless your skimmer is fed exclusively and directly by your drain from the display tank, your skimmer will always "miss" some of the water flowing through your sump. This will happen regardless of what your flow rate is or what the skimmer can handle. Most people have other things in the sump that you want the water to come in contact with, i.e. a heater, filter sock, carbon, GFO, etc. Higher flow through the sump will guarantee that your skimmer is always pulling water that needs skimming and will allow more efficiency for most of the other items in the sump. The more volume that flows through a filter sock, for example, the better the water has particulates removed.

Bottom line for me is the typical sump setup does not provide for a way to direct all of the water that enters the sump to go through the skimmer so why would you want the skimmer pump gph and return pump gph to match?. That would guarantee you that the sump would be "underfed", so to speak.

 

[Kyle918]

In my limited experience, I found about 5x the DT water volume through to be acceptable for my tank. Realistically, it's just about 6x the turnover of the DT.

This is for a number of reasons though. I do not have a skimmer so I'm happy to leave that debate for someone else.

The things I took into consideration in choosing a speed for my sump turnover are the following.

The length of my overflow - 24inches. If it was longer, I'd have more flow
Heating - a lack of flow can equate to lack of heat for the DT, especially at night when I crank my ac down.
Extra aeration. The flow of water to and from the sump helps to aerate the water further.

Lastly, the bubbles were annoying. I found afterwards that the distance between the baffles in relation to the speed of water flow plays a huge part in its effectiveness at trapping bubbles. The less distance between the glass, the faster the water travels through the baffles. If this is the case, bubbles may be forced down and under the baffles instead of floating to the top to pop.
Also, the size of my return section. I can't increase the speed much more otherwise my sump return section level drops a tad and a bit lower than I'm comfortable with.

So. To be completely honest about it, it comes down to your particular tank and sump setup. Figure out what you need for your tank and figure out what your sump can and can't handle in regards to the bubble trap actually trapping or passing bubbles based on the flow.

 

[usmc121581]

I never worried about turnover, I installed a ball vavle on my return lines and slowly tweaked it until I got the flow that worked for me. I havent touched the ball valve in 2 years and I have no clue what gph I have flowing through my sump.

 

[Reefer54]

I like to think about it like the rain. If it is raining 100 drops per sq ft per second, the person running to get in the door is going to get more wet than the person walking, simply because they are covering more sq ft per second. of course there is a threshold, but this can be applied to surface area in a sump, the water moving faster through the sump will cover more surface area.

 

[M_Jaco]

I like to think about it like the rain. If it is raining 100 drops per sq ft per second, the person running to get in the door is going to get more wet than the person walking, simply because they are covering more sq ft per second. of course there is a threshold, but this can be applied to surface area in a sump, the water moving faster through the sump will cover more surface area.

yes this is true, technically more surface area will be covered/hour, but is that good or bad?

You gotta look at it in terms of time too. Just because the water is flowing, doesn't mean the bacteria is acting on it. The longer the water is on contact with the surface area, the more the bacteria can react with the chemicals carried by the water.