Flow vs Turnover

[marco67]

Lets have some discussion that may clear up the confusion for newbies or just for the halibut.

So often I see posts on RC: I have 900X turnover rate in my SPS system .....LOL It's always some guy that just put a pair of tunze or the like in use so he does the math @ 40,000 GPH in a 75 ....
or you see "well my return pump is a xxx and 3 magdrives on closed loops and ..etc so my turn over is ..."
Anyway if this were turnover those tanks would look and sound like a toilet flushing.

Turnover = the number of times you pump your total system volume to the display and back to the sump. (10X is a good rule of thumb depending on system size and skimmer design)

Flow= much more complicated, lots of people just take the rating of the pump and divide by tank size and call it x/ hour. I think it really has as much to do with your aquascaping and type of pump as it does rating.
And !... service schedule....If you put a 500GPH power head in your tank 6 months ago how much flow do you have now ? NOT 500!


any way maybe this sounds stupid ...Maybe too basic...but maybe it will make for a good discussion.

 

[NanoReefer]

I agree, this should be clarified for everyone. Matt L. should be able to provide some insight. Also see here for some really good info that's related from Matt's presentation at a meeting:
http://www.bostonreefers.org/forums/showthread.php?t=10444

Looking forward to reading this thread as I am currently upgrading to a larger tank.

 

[Scuba_Dave]

So if 10x is good turnover for a tank why am I getting a ration of BS for trying to put a 2100gph pump in my 180G?
Instead people say I should only have 8-900 gph - approx what my skimmer can handle.
I like to save electricity...but I really hate buying pumps

 

[marco67]

are you dumping 100% of your water through the skimmer ?
if not then why would you size the return pump by the skimmer?

BTW if you are talking about the dolphin/ampmaster 2100 I have one running a 180 + 92 in a resturant and I love it! great flow, quiet and IMO a nice combo.
Oh wait the Amp 2100 is actually like 2500 GPH at 4 or 5 ft ..... (but I can't see the top of my head right now so that may be off a bit)

 

[Scuba_Dave]

No, I've been looking at the Sequence SW3200 model
Pushing from the basement I think I figured around 2100gph - but I may be off

 

[marco67]

Nice pump ....but if your going to loose that much to head....I wonder if there is not a better choice?

 

[NeO]

OK David,
lets say you are using the new EURO-REEF CS180 Rated for aquarium systems of +/- 180g (I dont know what skimmer you have). This skimmer has a GEN-X 4100 pump that drives 1085gph with ~237gph is air.
This means that from the 2100gph from your return pump only ~1/3 would be going through the skimmer and the other 2/3 will be going back to your tank without going through the skimmer and probable with lots of bubbles.
What we try to tell you on the other thread is that you will waist a lot of energy and your tank is not going to run the way it would if you use a small pump.

Gustavo

 

[denvig]

What is going on in a sump that is so special that it needs 2000 GPH or more going through it 24/7? Does anyone keep Acro’s in thier sump? I just don’t get it.

 

[Scuba_Dave]

We've been thru this
I have 1400gph+ going thru a 30/40g sump

My skimmer pump handles approx 8-900gph

No bubbles what-so-ever
No baffles - none

If my return pump dies I still have my Tunze in the tank for circulation
If my Tunze circuit kicks out, then with a low flow return pump I have very low flow thru my tank - but probably still enough to keep things alive

Getting more flow to the sump/settling tank means more waste exported from the main tank. Even with 5x the flow (900 gph) going out of the tank, you are not truly getting 5x the turnover - some of that water has already been thru the sump
If you pump 90g thru...you now have 90g of original water...90g of "processed" water
Pump another 90g thru...you now have 45g of original water...135g of "processed" water

etc etc..law of diminishing returns...I'm sure somewhere there is that "sweet" spot of the optimum turnover. But on what is everyone basing there decision?
A guess? The new fad? Before DSB were in...now maybe out. High turnover was in..now out...?

 

[denvig]

I don't know if high turnover was ever in. Hi flow was and still is. IMO it just dosent need to go through the sump.

 

[Scuba_Dave]

Again...on what is everyone basing there viewpoint?
Any data..tests...or just I think?

 

[NeO]

Getting more flow to the sump/settling tank means more waste exported from the main tank.

OK, The water has been exported to your sump and then what?
went right back to your tank and has not been processed by anything!!

 

[NeO]

Again...on what is everyone basing there viewpoint?
Any data..tests...or just I think?

May I ask you the same question?

 

[Scuba_Dave]

Getting more flow to the sump/settling tank

 

[Scuba_Dave]

May I ask you the same question?

Based on the amount of detrius that I am able to vacuum out of my sump
and my skimmer output

 

[Chris L]

ok i am not an expert by any means but if you are pumping the water from the sump back to the tank at such a high rate it seems that all you are doing is increasing your total water volume ( which is not a bad thing ) and not using the sump for anything more then an excess water storage container.

 

[Matt L.]

Flow versus Turnover

People want to get a handle on just how much agitation there is in their tank, how much the water is moving around.

People tend to turn to the hydraulic properties of Flow and Turnover Rate. The problem is, both flow and turnover rate really don't do a very good job at telling you how much agitation there is in the tank.

First, here's a recap of flow and turnover rate:

• Flow: Flow (Q) is the volume of water your pump generates (V) in a given time t (t). Flow is just the velocity generated multiplied by the time in wich that belocity was generated. In mathematical form, Q = V x t. Mind you, this is the volume generated, not the volume of the tank, and the time in which that volume was generated.
  
• Turnover Rate: The technical term for this is hydraulic residence time. It is represented by the greek letter theta (θ) which I guess is kind of like a letter 't', but here, we can just use HRT. The units for HRT are per time, as in turnovers per time. A turnover is the average amount of time a particle of water spends in a defined volume (V), such as your tank. In mathematical form, HRT = V / Q.

So you see, turnover rate and flow are kind of similar. They are based on the same basic variables, and thus, they suffer from the same limitations.

What reefers really want to know is how much water agitation there is in their tank.

There is a better parameter for this, although not by much. It is called the velocity gradient G:

This equation is kind of hard, but G is the velocity gradient, which basically gives you a number per second.

In the equation above, P is power. This would be the total power in terms of flow being input into the tank, including the main recirculation pump discharging to the tank and all other pumps and powerheads inside the tank. Power is in Watts. The letter u is the dynamic viscosity of the water, which for saltwater at 60F (best I could do) is 0.00120. Oh, and the volume V is in cubic meters.

The good thing about the velocity gradient is that it enables you to sum the power beiing input. If you have flow through a tank with one recirculation pump and a bunc of powerheads in that tank, you can't just add the total power, and the hydraulic retention time is not affected by the powerheads which recirculate water only in the tank. However, all you would need to do is add the power of the main recirculation pump and all the powerheads to get the velocity gradient.

Matt

 

[Liam]

What is going on in a sump that is so special that it needs 2000 GPH or more going through it 24/7? Does anyone keep Acro?s in thier sump? I just don?t get it.

I agree hi turnovers through the sump are a pain in the a** to handle but my theory is that you can greatly improve gas exchange by moving alot through the sump.

 

[RichConley]

Flow= much more complicated, lots of people just take the rating of the pump and divide by tank size and call it x/ hour. I think it really has as much to do with your aquascaping and type of pump as it does rating.

I can't agree more. 3000gph in a tank with nice open rockwork is more effective than 5000gph in a tank that is a "pile of rocks"

 

[Scuba_Dave]

Lets have some discussion that may clear up the confusion for newbies or just for the halibut.

any way maybe this sounds stupid ...Maybe too basic...but maybe it will make for a good discussion.

1st part may not be working Marc, but 2nd part is!!

Aeration is one good point, Cooling effect is another, my basement is a cooler
I'll end up having 180g show, 129g sump, 125g frag. 75g fuge

So 900gph would give me 5x turnover in the display
BUT, only approx 3x turnover in basement

2100gph would give me over 10x turnover in the tank - still not a TON
and 8x turnover in the basement

I'd prefer the $$ saving lower flow pump....in fact that is what I'm buying
But I'm really hoping this isn't a big mistake
I do hope I won't be pulling this pump back out in 2 months

and YES..people DO grown SPS & Frags in a basement setup.
Is that really that hard to understand....?