Dumb Water Flow Question

[PScoggin]

For any of you "experts" out there, I've got a pretty basic question regarding water flow that bothered me for some time... I have a 90 gal tank; with all of the displacement by LR, substrate, etc., the true water volume in the system is about 60-65 gallons (55-60 in tank and aboout 5 in the sump. Looking at redesigning my filteration system for a tank makeover, Ive determined that I want a turnover rate of about 10X. My question is this: are turnorver rates calculated on total tank capacity (90g) or actual water volume (55-60g). Should I be shopping for a pump with a capacity of 900 (90 x 10) or 600 (55-60 x 10) gph?

Thanks in adavnce for your input.

Regards-
H2ORat

[Nek]

If you want a 10x turnover of water volume, I would by a pump based upon the amount of water in your tank. In your case, 60-65 gallons. (I personally would go bigger.:) )

[aquaman67]

I agree, go with actual volume...who has an empty tank anyway???

[astrogazer]

I too would go for more flow, but if you're looking for actual numbers, you're not flowing LR you're flowing water so 65 would be the target number.

[PScoggin]

OK so the actual volume is the way to go... As to the suggestions for higher flow, it this still appropriate if the final plan is devoid of SPS corals? I know that these require huge flow rates for success, but my plan is to keep mostly softies, inverts and a few fish. Does anyone have a legitimate agument that a flow rate of 10X is insufficient?

H2ORat

[getwet]

I am going to disagree, but mostly because I want to hear WHY everyone seems to think it should be total water volume.

Anyway, the point is this... if you had a 500 gallon sump on a 50 gallon display why would you want to recirculate 5500-11000 gallons on the poor 50 gallon display. Your bio load is limited by the volume in the display tank (or should be). Now perhaps you need more than 10x the display volume, but it seems to me you should be looking at recirculation of your display tank volume (and probably the volume not taking into account live rock, sand, etc. as these amounts vary on the types and amounts you have).

Anyway, these are just my random thoughts.

[SeaStar]

I think getwet makes a good point. However, as is the case with the original poster's setup, other than his 5 gallon sump all his water volume is his display tank. So going with the actual gallons of water in that system (65 in this case) that would be the target # for 10X turnover.

[eums]

i would go with more flow. i have a 55 gal witha maybe 35-40 gal of water in it, no sump with about 1500 + gph worth of flow, 40 something turn over rate. its allmost enough, if i wanted any more i would need to take all the LPS out.

[dor]

Getwet's point is maybe valid in some way but I'd disagree that the bio load is only the 50 g in the display tank.Your total volume is what takes the bio load not just the tank.
And you just wouldn't run a 500g sump with a 50g tank you need the flow in the sump and the tank not just the tank, if you follow.
I'd base your calc. on the total volume of your system, sump and all.Then try and turnover the tanks volume 10-15 times and if you need more flow later just add a powerhead or two.
I'd always go over the top a little with the lift pump and just restrict the flow as required with a gate value or something like, then you have control, you have extra if needed when thinks start to slow a little.
just my two pennith.
have fun.

[PScoggin]

Originally posted by getwet
... Your bio load is limited by the volume in the display tank (or should be)....

First off, thanks to all for the input. I don't know that I'm any closer to the "right" answer, but it's sure helped develop my thought process on this topic.
Since it was brought up, I know have another question. Does the water volume really have any direct impact on determining the tank's bio load? I've always thought that the bio load was determined by you system's ability to denitrify waste (i.e. amount of live rock/sand, trickle filteration, etc).
Again, thanks to all.

H2ORat

[getwet]

In short...yes.

Bioload for aquarium purposes is the capacity for a system to handle the wastes produced by the animals, leftover food, etc (waste). Increasing the volume allows a larger capacity because it dilutes out those wastes and allows a smaller system to deal with much more waste than it might otherwise.

As to your original question. I think Seastar had it right. It's a 90 gallon tank with 65 gallons of water and a 5 gallon sump. target a minimum of 700 gallons/hour, 1000 would be better. But just to make it fun, this could change depending on what's in your tank. Seahorses? SPS? FO? How many?

I still maintain you should be basing it on tank size not total system volume though. The assumption is that the water coming from your return line is "conditioned", whatever your filtration method. So in your tank if you needed 1000 gallons of flow per hour, it's irrelevant if the sump is 5 gallons or 1000 gallons, as long as the water is "conditioned".

I think the other interesting aspect is it is really a combination of turnover volume (new water coming in) and current needed.

I find it absolutely fascinating that such a simple question is soooo complicated. But then, I'm easily entertained.

[PScoggin]

If there's anything that I've learned in this hobby, it's that there are no short, simple answers to ANY questions. Unfortunate, in that I'm a staunch advocate of the KISS principal... always seeking the simplest solution that resolves the issue.

[pam7049]

Ok, I feel kinda dumb asking this, but how do you calculate GPH?? I have a 30 gal, with about 30lbs of LR and a 3in bed of sand (so not sure how much water). I have tons of water flow, but I never knew there was a science to it. :P

[blaze422]

not to hijack this thread, but if I have a small overflow box hanging in the back of my 120 gallon tank, and was told that #1.....poor idea for a large reef tank, and #2 need to increase circulation...Can I put another over-flow box and "T" the hose from the sump to push 1000 GPH from one pump into two boxes ?

[MadTownMax]

I would go with as much flow as you can handle.

Of course this is dictated on what you have. Like Getwet said, if you have seahorses, that's your limiting factor. Fish are said to be more healthy with more water flow, and it will definately inhibit cyano growth.

Go with an over-sized pump with many outlets in the tank(4-6 would probably be ideal for the best random water movement, or a couple sea swirls) Something like a Dolphin 2000 or maybe a mag 24 (mags are severely limited when it comes to head pressure)

If it's too much - tune it down w/ a $5 ball valve (Mag-drives would not be your best option here, as the head pressure would decrease the life of the pump), but if it's not enough flow, you'll want another pump ($$$)

I've got a mag 9.5 on my 72, and I'd love to have about 2X as much flow, with 4-6 outlets, instead of the 2 I have now.

Have I added enough to the confusion ; ).

[PScoggin]

Originally posted by pam7049
... how do you calculate GPH?

Total water flow, represented in gallons per hour (GPH), is simply a combination of the total output of the combined pumps within your system such as the main return pump (less head loss... a nifty calculator is at http://malhavoc.homeunix.com/head/), any powerheads used for circulation, and/or closed loop pump (though there is generally no loss for vertical lift to be calculated as with the main return pump, you do have to account for losses due to restrictions caused by the plumbing).
The general school of thought is that you should move a minimum of 10X your system's water volume per hour. If you're not sure of the exact volume contained in your system (who can be sure based upon the various responses/comments within this thread?), be conservative and use the tank's capacity (i.e. 30 gal) and multiply by 10 (or 300 gph as a minimum goal). I've also seen some systems with claims of 40X or better. Much also depends upon what you are/planning to keep in the tanks as different inhabitants have different flow preferences.

H2ORat