How slow is too slow through sump?

[EllisJuan]

I have been playing with the setting on my new Jebao DC3000 return pump today. I have a 65g DT with a 24x15x12 sump. I do not have a refugium. As I slowed down the return pump I noticed a couple things that I liked. My filter sock looked less overwhelmed, there were fewer microbubbles entering the sump, and the bubbles that are there from my skimmer and return have more time to pop in my bubble trap. I would also think this gives my water more contact time with the skimmer and also my Phosban reactor.

Right now I am running the pump on the 2nd from lowest setting. Which from what I have gathered is about 65-70% rpm/power.

So my question, is there any negatives to running this slow through the sump?

 

[Mark Bianco]

IMHO I like to keep the flow thru the sump at about 5 times the total water volume. The only negative I can think of if you do not have any powerheads or enough flow in your tank that will keep the detritus in the waterflow and be able to be carried away back to the sump where your skimmer can help remove it.

Mark

 

[smsadmin]

I have always felt that flow through the sump should be slow. Return lines should not be what you use to depend on flow through DT. Wave makers and power heads are there for that. I know you don't have a fug, but still should be slow enough for protein skimmer and reactors to have a chance to do their job.

 

[EllisJuan]

IMHO I like to keep the flow thru the sump at about 5 times the total water volume. The only negative I can think of if you do not have any powerheads or enough flow in your tank that will keep the detritus in the waterflow and be able to be carried away back to the sump where your skimmer can help remove it.

Mark

That is my thought also. I actually slowed it down a little after adding another powerhead knowing that the flow in the tank was strong enough. I am running a Jebao WP25 and WP10 on a dual controller in the 65g.

 

[CoopsReef]

I would say less than 3 times total water volume is to slow.

 

[Reefvet]

I would say less than 3 times total water volume is to slow.

Why ?

Based on what ?

 

[Octobot]

Assuming you have power heads in the DT you are using for primary in-tank circulation, rendering the relatively low flow coming from the return pump negligible...

Ask yourself, "what is the purpose of my sump?". Chances are you have a skimmer and maybe some kind of filter media. For most, the skimmer is the primary purpose of the sump - so what is the best flow rate for your skimmer? That's the real question here.

If your skimmer's pump is running at 500gph, for example, and your return pump is running at 300gph, then your skimmer is not running as efficiently as it otherwise could be due to its pump skimming at a faster rate than the return pump is providing water.

My sump's main purpose is to house my skimmer. My return pump matches the flow rate of my skimmer, so I know I'm getting all the efficiency out of my skimmer as possible and my sump is doing its job.

 

[Octobot]

These "3 or 5 or 10 or whatever number times the total water volume" claims are baseless and useless. A more-or-less random rule of thumb that no one seems to be able to remember where it came from or why they adhere to it.

Have reasons for what you do!

 

[FlyPenFly]

If you have a big skimmer you need to keep it fed of organics or the foam heads will constantly collapse and be inefficient.

 

[CoopsReef]

How slow is too slow through sump?

Why ?



Based on what ?

If you only have 1 time turnover which would be 65 gph everything would almost be standing still. Same for 2 times turnover(130 gph) water would basically just be trickling out. If you have say 10 times turnover my guess is that you would have micro bubbles everywhere. I don't believe using your return as your main water flow source is very efficient.

 

[Octobot]

I would argue it's not as efficient as it may at first seem. Typically, it will be necessary to use multiple power heads throughout the tank to eliminate dead zones. One pump will not suffice in this regard. At this point, the return pump is only one of many other pumps... So why force yourself to use the least versatile pump in your arsenal (the return) to do all the circulating when you could use the versatility of power heads to get just the right amount of flow exactly where you need it?

Relying solely on the return isn't an even efficiency trade imo - and having a flow rate thru the sump that is X number of times the system volume means nothing to the sump itself and it's functions.

 

[ca1ore]

Assuming you are not relying on the main return pump for any in tank water flow (and you shouldn't be; power heads are much better for that) then if you think about it, all that needs to be accomplished is adequate surface skimming of the display and uniform temperature (again assuming heaters are in the sump; and why wouldn't they be) between the sump and display. Beyond these things, too slow or too fast is simply in the realm of personal preference. With trial and error, over many years and tanks, I have arrived at the opinion that about 3x tank volume through the sump hourly suffices to meet both key criteria. My currant tank is a 265 and I'd estimate that flow through my sump is in the 800 gph range.

Things like matching sump and skimmer flow, which are often touted as arguments for higher flow, are completely without merit IMO - or at least I've never read a cogent augment as to why.

 

[Octobot]

Things like matching sump and skimmer flow, which are often touted as arguments for higher flow, are completely without merit IMO - or at least I've never read a cogent augment as to why.

If your return pump is transporting water at a slower pace than your skimmer, then water that has already been stripped by the skimmer will accumulate in the sump. This in effect creates an environment where the water in the sump stays cleaner than the DT, rather than equalizing. If you're cleaning water that is already clean, that means you are not spending that time cleaning the water that is unclean.

You could exaggerate this effect by exaggerating the difference in flow between the two pumps. If you cannot imagine a skimmer pump at 500gph in combination with a return pump at 300gph being an inefficient environment for the skimmer, then imagine a skimmer pump at 500gph in combo with a return pump of 1gph. Apply this to a large tank, and you can see how the sump's water would be re filtered over and over again, but the entire system volume would take ages to cycle all the way thru. In this situation, even though your skimmer is of suitable size in relation to your system, your return pump would be undermining its efficiency.

 

[ca1ore]

If your return pump is transporting water at a slower pace than your skimmer, then water that has already been stripped by the skimmer will accumulate in the sump. This in effect creates an environment where the water in the sump stays cleaner than the DT, rather than equalizing. If you're cleaning water that is already clean, that means you are not spending that time cleaning the water that is unclean.

This is exactly the kind of reasoning I see all the time that actually makes no sense to me; so I'm still waiting for that elusive cogent argument. No skimmer that I have ever used is so efficient as to remove all the organics it can with a single pass - and I've used some monsters over the years. After all if it were possible, why would recirculating skimmers even exist. The reality is that skimmers must process water many times to strip as much of the organics from it they are capable of (about 30% based on studies I have read) so at reasonable flow rates there is likely to be no differential levels of organics between the sump and the tank whether rates are matched or not. OK, if you were to take things to an extreme and have such a slow flow from the tank as your 1 gph example, and that might actually not be slow enough, then it is probably reasonable to assume that could reduce the efficiency of the skimmer.

 

[EllisJuan]

My SWC 150BMK skimmer has a Atman 2500 pump rated at 700gph. I have no desire to run 700gph through my sump. I am pretty sure my overflow could never run 700gph. So far I have not seen any issue with my skimmer not being able to keep its bubble head. It is pulling nice dark skimmate.

 

[ca1ore]

My SWC 150BMK skimmer has a Atman 2500 pump rated at 700gph. I have no desire to run 700gph through my sump. I am pretty sure my overflow could never run 700gph. So far I have not seen any issue with my skimmer not being able to keep its bubble head. It is pulling nice dark skimmate.

Nor will you! For a 65 gallon tank, you'll be fine with 200 gph through the sump, regardless of how much your skimmer pump is rated for. You can certainly run more water through your sump; it won't do any harm, just burns more electricity.

 

[Octobot]

If it is logical to suppose this happens at a more extreme difference in flow rates, it is logical that it happens some amount less at a lower flow rate. It is illogical to assume the problem vanishes into thin air.

Also, organic molecules differ in how readily/quickly their chemistry will allow them to make their way up the chain from the skimmer pump to the skimmer cup as they ride air/water interfaces via foam. Some take quite a long time, others less. Because your skimmer continues to pull organics over time and longer than a single system volume turnover is in part due to it taking varying lengths of time to extract different types or organics out. It's also worth noting that a 'total system volume turnover' is not 'total water turnover'. Skimmed water mixes back in with DT water, so although you've run your total system volume through your skimmer over a given period of time, some of that water had passed through more recently than other bits, and some bits never passed through at all.

 

[ca1ore]

If it is logical to suppose this happens at a more extreme difference in flow rates, it is logical that it happens some amount less at a lower flow rate.

Doesn't seem logical to me at all!

Also, organic molecules differ in how readily/quickly their chemistry will allow them to make their way up the chain from the skimmer pump to the skimmer cup as they ride air/water interfaces via foam. Some take quite a long time, others less. Because your skimmer continues to pull organics over time and longer than a single system volume turnover is in part due to it taking varying lengths of time to extract different types or organics out.

Whether that is really true or not (link to research?), it actually is counter to the argument of matching sump flow to skimmer flow.

But, frankly I have no great interest in trying to dissuade anyone from doing what they think is best, I just find this to be one of those perpetuated myths that experience ultimately proves unfounded.

 

[Octobot]

My SWC 150BMK skimmer has a Atman 2500 pump rated at 700gph. I have no desire to run 700gph through my sump. I am pretty sure my overflow could never run 700gph. So far I have not seen any issue with my skimmer not being able to keep its bubble head. It is pulling nice dark skimmate.

Passing less water to your skimmer than what it can handle doesn't necessarily mean you should expect no skimmate. This also has to do with the concentration of organics in your tank. A skimmer running less efficiently in water heavily concentrated in organics may collect just as much skimmate as a skimmer running more efficiently in water with few organics present.

My question would be if I'm consistently skimming very heavy skimmate - where is that skimmate coming from and why is it always so heavily concentrated? One possible explanation could be that my skimmer is not running efficiently, and those organics have backed up and saturated the water. Though there are surely many other possible explanations too, such as heavy phyto feeding for example, but I'm using that to illustrate the point.

Personally I wouldn't want heavy skimmate 24/7 - because that would imply to me there are high organics in the water 24/7 when I paid good money for a skimmer to prevent that from happening.

 

[Octobot]

Doesn't seem logical to me at all!



Whether that is really true or not (link to research?), it actually is counter to the argument of matching sump flow to skimmer flow.

But, frankly I have no great interest in trying to dissuade anyone from doing what they think is best, I just find this to be one of those perpetuated myths that experience ultimately proves unfounded.

I don't think you understand the things you think you understand.

But since you have no great interest and take pride in ignorance, have a good day!