anyone have an answer?

[ScottM]

I continually read on RC how people confuse Flow with turnover rate (I was even having a discussion about it earlier today). My question is regarding turnover rate. For arguments sake I am defining turnover rate as the amount of water that transfers from the tank to the sump and back to the tank. NOT the GPH flow INSIDE the tank.

I constantly hear and read that a reef tank minimum turnover rate is 5x total volume per hr and the ideal turnover is 10x total volume per hr


where did the ideal 10xHr of total tank volume turnover come from as a "guideline" for a reef? Shouldn?t the turnover rate be determined by the skimmers pump GPH rating?


Let?s say my system is 275g (total water volume in system minus rock sand etc...) and my skimmer Pump is rated at 1000gph.

Wouldn?t my ideal turnover rate be 1000gph instead of the suggested 2750gph? Or close to it? The only reason for a variation I can conceive is that the skimmed water is constantly mixing with unskimmed water. Is there a standard ratio for this variation that we could apply to the calculation?
Let?s assume for the sake of argument that I am running the Berlin method with an in-sump skimmer rather than the pictured external skimmer flow design. Also assuming a Refugium is not present.

why no fuge? I would be inclined to believe that a fuge would allow an even lower turnover rate because the macro present in the fuge would only increase the systems ability to process the bioload. Almost as if the size of the fuge could be directly translated into an increased GPH for the skimmer


ANYONE?......


Does someone have the BRS library copy of:
Aquatic Systems Engineering: Devices and How They Function" by P. R. Escobal.
Would love to get my hands on it.

Thanks

 

[etszoo]

That's why you want that book. Sorry too technical for me. I'm still hydrating after
last night....need more sleepy.

 

[Scuba_Dave]

I'm not up on the technical explanation, but as someone (Matt?) has said, our aquariums are effectively a closed system. My turnover rate to my sump used to be ~1450gph for a 125g. I am now diverting some of that to a cannister filter (charcoal) & will eventually divert 1/2 to a skimmer.
So my flow to the sump will remain the same (1450 gph), but only ~700gph will flow directly back to the tank. In the tank I have a Tunze (1850gph) w/controller.
I think there are many different ways to go about this. Is one way better then the other? Maybe. But I think it should be based on what is working, not any etched in stone "rule"
Let's use my former tank, 60g hex as an example. 60g I should have had min 300gph, and up to 600 gph. I had a 400gph pump on the system. I had cyano. I added a skimmer & increased the flow in the tank to ~20x =1200gph. Cyano problem ended.
My sump was a very basic sump ~5g, so what was it doing for me?
Water aeration, I kept one heater in the sump, grounding probe, and I used it for top off. Pumping 400gph = 6.7gpm min, which means the water was spending less then a minute in my sump.

What about sumpless systems? no turnover whatsoever!! So are they a failure? For myself I think a combination of the two works best. As long as I don't have cyano or detrius hanging around, then I have enough flow/turnover and skimming.
I personnally think the "ideal" skimmer setup is taking all of the water that is coming from the tank, skimming it, then returning it to the tank.
If you are reskimming the water you have already skimmed (ie the water goes back into a large sump that you are skimming), then you are not skimming
optimally.
And isn't flow in the tank very beneficial as it "forces" the live rock to filter water?

 

[Matt L.]

Turnover Rate

Scott,

Turnover Rate is related to hydraulic retention time (HRT). Turnover rate is actually 1 divided by the HRT. It is better to first explain HRT, and then discuss turnover rate.

As our reef tanks are closed systems, when people refer to HRT, they are typically referring to the main display tank. HRT is defined as the volue of a system divided by the flow rate through the system:

HRT = Volume / Flow

If you notice, HRT will have units of time. But other than a fancy name, what is HRT? HRT is the average period of time in which system fluid (tank water) resides in a set space, such as your tank.

Therefore, turnover rate is:

Turnover Rate = 1 / HRT = Flow / Volume

As an aside, when people talk about turnover rate, they are probably referring to their main display tank. In our systems, any space that has an influent and effluent flow has a HRT. Your calcium reactor, skimmer, refugium, and sump also have HRTs.

To do an example, lets say soeone has a 100gal tank that drains to a sump, and there is a pump in the sump that returns water back up to the main display tank. Let's say the pump operates at 500 gal/hour under the conditions present (the person has a flow meter to measure). The HRT for this system is ( 100 gal / 500 gal/h ) = 0.2 hours, or 12 minutes. If you averaged up the time every infinitesimally small volume of system fluid spent in the 100 gal tank, it would be 12 minutes. Some may spend a longer time there, others may spend a shorter time, but the key is that the average is 12 minutes.

Turnover rate, being just 1 / HRT, is ( 500 gal/h / 100 gal ) 5 per hour. This makes sense. On average, every infinitesimally small volume of system fluid enters and leaves the tank five times in an hour, or every 12 minutes.

I hope this helps,

Matt

 

[ScottM]

Let's use my former tank, 60g hex as an example. 60g I should have had min 300gph, and up to 600 gph. I had a 400gph pump on the system. I had cyano. I added a skimmer & increased the flow in the tank to ~20x =1200gph. Cyano problem ended.

i would consider the cyano to be a result of inadequate circulation inside the tank as well as the lack of nutrient export (skimmer)
WHERE did you get that you SHOULD HAVE HAD MIN 300gph? this is my whole question. why does this standard exist? WHY SHOLUD I PAY 120.00 A YEAR TO RUN A MAG 12 WHEN I CAN PAY 50.00 A YEAR TO RUN A MAG 5?

What about sumpless systems? no turnover whatsoever!! So are they a failure? ?

not failures, why because they have are likely to have a Hang on back skimmer that can export nutrients. this only supports the basis of my original question. Why is this "standard turnover rate" not directly related to the skimmers GPH ability?

And isn't flow in the tank very beneficial as it "forces" the live rock to filter water?

it's very beneficial but i am focusing on turnover rather than flow. They are related but serve different purposes.
the primary function we send our water to a sump is to export wastes via a skimmer. shouldn't our delivery of water be determined by our skimmers ability to process the water? (gph)
flow inside a tank has many more factors that can not be as easily equated to GPH. ie: aquascaping, size, shape, coral type.... etc. this i why i eliminated the fuge for this example.
whereas turnover rate can be directly related to a specific contant (gph) of the return pump and the skimmer pump.

 

[ScottM]

Scott,
Turnover rate, being just 1 / HRT, is ( 500 gal/h / 100 gal ) 5 per hour. This makes sense. On average, every infinitesimally small volume of system fluid enters and leaves the tank five times in an hour, or every 12 minutes.
I hope this helps,
Matt

you've explained turnover rate, but i want to know:

where did the ideal 10xHr of total tank volume turnover come from as a "guideline" for a reef?
Shouldn?t the turnover rate be determined by the skimmers pump GPH rating? if not why?

 

[denvig]

From what I have read it is the flow rate inside the tank that is important not how much goes through the sump. The flow or turnover is for the benefit of the tank inhabitants not the skimmer. A 10 time turnover (Flow rate) is the current minimum for a reef according to the latest thinking. I believe this also depends on what is in the tank and what are it?s needs. Check this site out there is a lot of info here.

http://www.wetwebmedia.com/circmarart.htm

 

[ScottM]

From what I have read it is the flow rate inside the tank that is important not how much goes through the sump. The flow or turnover is for the benefit of the tank inhabitants not the skimmer. A 10 time turnover (Flow rate) is the current minimum for a reef according to the latest thinking. I believe this also depends on what is in the tank and what are it?s needs. Check this site out there is a lot of info here.

http://www.wetwebmedia.com/circmarart.htm

case and point.
This link covers everything about Internal tank flow example: Tunze streams.
it even refers to the internal flow as "turnover rate" but says nothing about a skimmer or its effectiveness.

From what I have read it is the flow rate inside the tank that is important not how much goes through the sump

by the amount of skimmate i remove on a daily basis i'd be willing to bet that how much goes thru the sump IS important.

 

[denvig]

by the amount of skimmate i remove on a daily basis i'd be willing to bet that how much goes thru the sump IS important.

Yes Scott I also think this is very important. You do want the skimmer to have access to all the tank water but you don?t need it to go to the skimmer at a rate of 10 times the tank volume per hour.

 

[jango]

alright scott you got me thinking,wouldnt the ideal flow rate for your return be the same as the flow coming out of your skimmer so you would always be pumping clean treated water back to the tank instead of just pumping it through your system.internal flow rate for the tank should be out of the question,so my thoughts are whatever your over flow puts in your sump your skimmer should atleast put out the same if not more and your return pumps should put out the same as the skimmer that way you would clean all the water befor eit goes back to the display...
i am still an infant to this hobby but that seems how it should work...IMO
but then again i have no clue what i am writing about...i am running a tank with no sump and a bakpak

 

[ScottM]

Yes Scott I also think this is very important. You do want the skimmer to have access to all the tank water but you don?t need it to go to the skimmer at a rate of 10 times the tank volume per hour.

so your sump "turnover rate" is ???

alright scott you got me thinking,

that's why i posted the question

wouldnt the ideal flow rate for your return be the same as the flow coming out of your skimmer so you would always be pumping clean treated water back to the tank instead of just pumping it through your system.

so if you have a Euroreef with a 350gph pump (ksp3500) then you only need 350gph flowing thru your sump......

internal flow rate for the tank should be out of the question,so my thoughts are whatever your over flow puts in your sump

this is determined by your return pump

your skimmer should atleast put out the same if not more and your return pumps should put out the same as the skimmer that way you would clean all the water befor eit goes back to the display...

MY POINT EXACTLY

..i am running a tank with no sump and a bakpak

so if you added a sump and your bakpak is rio400 pump (145gph) then you would only have to have 145gph moving thru your sump.......

 

[jango]

alright that makes to much sense,now i think i might rethink how im going to setup my 75,maybe the t4 will go on a closed loop with the OM then get my return and skimmer pumps the same...so what goes in the sump goes right in the skimmer and right back to the tank without water bypassing the skimmer...

 

[denvig]

Scott you are talking about two different things that I don?t believe have anything to do with each other. The flow and tank volume turn over is for the corals etc in your tank. The skimmer is there to skim nutrients out of the water column. The size and flow of the skimmer is designed by the manufacturer for the intended size tank. Even if you put the skimmer in the tank the water going to it would always be mixed with un-skimmed and skimmed water. It doesn?t matter as long as the skimmer is the right size for the tank. The only way for all water exiting the sump to have gone through the skimmer first is for the tank return to be plumbed directly into the skimmer before entering the sump. This of course would be very difficult if not impossible to do, as you would need a return pump that matches exactly that of the skimmer output.

 

[Piscevore]

You just would need one big f-in skimmer.

To answer your question scott, I think its just a rule of thumb. Its like 1lb of sand per gallon, or one inch of fish per gallon. It sets a minimum, or serves to provide for 2 different things. If you turn the tank over 15x per hour, a by-product of all that draining and pumping will be flow.

It isn't like you are adding new water, its the same old water. So I think turn-over and flow ARE related, in the context of your '10x' per hour rule.

Its snake oil. Use your Skimmer, your Tunze, and stop worrying

 

[Matt L.]

you've explained turnover rate, but i want to know:

where did the ideal 10xHr of total tank volume turnover come from as a "guideline" for a reef?

I'm glad I have cleared up HRT and turnover rate, but regrettably, I'm not sure what 10xHr stands for? Is that 10 times the hydraulic radius?

Regardless, that rule of thumb probably came from someone's orifice. Okay, that's a bit harsh. More likely, someone probably took a rule of thumb from industry, for better or worse, and applied it to fish tanks.

Shouldn?t the turnover rate be determined by the skimmers pump GPH rating? if not why?

IMO, no. I feel the HRT of the skimmer should be determined by its operating needs to process the waste load in your tank. What is that flow rate through the skimmer? I unfortunately can't tell you. Perhaps a manufacturer would shed some more light on the matter,

Matt

 

[Ray]

Ok now to put a twist into it.....well just a question but I am sure it will complacate things a bit more! What should the turnover rate be for a FOWLR??? Is it just as much as a reef?

 

[Piscevore]

Matt, you're a S.A. (no, not secular authority) :-D
I meant 10 times per HOUR thank you.
And the point to this thread is that no, contrary to popular belief, ReefCentral's "general" advice doesn't always pertain to some of the most up to date, modern, and experienced reefers (scott)...

 

[ScottM]

Its snake oil.

I think I am going to agree with you on that.
I get the impression that the MFG are "guessing" at a skimmers tank recommendation.
I think you/they should be able to quantify it mathematically.
Can they?


I should have titled the thread "lets talk about flow vs. turnover: why do I NEED a giant pump in my sump? "

Because as I read more of Reef Central's "general" advice, I feel like people are making Decisions based on opinions rather than a factual calculation.
I am sure I have told numerous people to use this pump, or that skimmer, but i want a FACTUAL calculation to base it on.

 

[ScottM]

Ok now to put a twist into it.....well just a question but I am sure it will complacate things a bit more! What should the turnover rate be for a FOWLR??? Is it just as much as a reef?

For the equation I am looking for:
It would be the same.
The return GPH from the sump is directly related to the skimmers ability to process the GPH.

The question FOWLR Vs Reef should be asked when evaluating what size skimmer your system requires.

Here I'm asking what size pump I need to efficiently use my skimmer

this is all jut food for thought.

 

[ScottM]

Regardless, that rule of thumb probably came from someone's orifice. Okay, that's a bit harsh. More likely, someone probably took a rule of thumb from industry, for better or worse, and applied it to fish tanks.

i agree with that and is exactly why i am questioning it. further more i am PAYING for it.
not only in addtional pumps but also in electricity.
on a 20g the issue may be a total waste of time. but on a 1000g system....
think scuba dave is going to be running a 7000gph return pump for his new giant 650g tank? i am willing to bet he's going to try. why? because everyone on RC tells him to. wheres the math behind it that says he should? if hi skimmer only processes 1500gph then why not run a 1500gph pump.
7000gph vs 1500gph..... i bet the pump mfg's are worried now.

Originally Posted by Scott Merrill
Shouldn?t the turnover rate be determined by the skimmers pump GPH rating? if not why? Matt-Davis Sq Posted : IMO, no. I feel the HRT of the skimmer should be determined by its operating needs to process the waste load in your tank. What is that flow rate through the skimmer?

i think this is the question you should be asking at the point skimmer selection for your system rather than pump selection for your return.....

I unfortunately can't tell you. Perhaps a manufacturer would shed some more light on the matter,
Matt

would that be a pump MFG or a skimmer MFG? think they will both give me the same answer?