Flow - How to Calculate?

[kiMxD]

Hello folks!

So I wonder if my way of calculating flow is correct, please see my math below and tell me if that sounds right or how you do it.

Total Water Volume: 95 gallons (75 tank + 25 sump);
Return Pump: Jebao 1320 GPH;
Wave Makers: 2x Jebao PP-8 2100 GPH.

Calculating Tank Turnover per Hour:

Total water volume: 95g
Return pump gph: 1320
Return pump strength level: 52 (out of 100 max)

100x = 1320
52 = x
100x = 68640
x = 68640 / 100
x = 686.40
x = 686.40 / 95
x = 7.22 times per hour

Calculating Water Flow per Hour:

Total water volume IN THE TANK: 75g
Waver maker gph: 2100
Wave maker strength level: 2 (out of 8 max)

8 = 2100
2 = x
8x = 4200
x = 4200 / 8
x = 525
x = 525 x 2 (2 pumps running) = 1050
x = 1050 / 75g
x = 14 times per hour

Please, let me know if my math makes sense, if doesn't, how do you calculate?

Also, if my math is right, isn't my water flow per hour rate too low?

Thank you!

 

[MarkW64]

I see at least two problems with your tank turnover calculation:

First, you should only use display tank volume. (actual volume not "tank size", and not include sump.)

Second, I assume that 1320 GPH is the return pumps "advertised" flow at zero head -- your actual flow would be less, even if running at max.

 

[billdogg]

I see at least two problems with your tank turnover calculation:

First, you should only use display tank volume. (actual volume not "tank size", and not include sump.)

Second, I assume that 1320 GPH is the return pumps "advertised" flow at zero head -- your actual flow would be less, even if running at max.

^^^This^^^, for starters.

Optimal total flow will also be dependent on the livestock you intend to keep. If it is a FOWLR, you could go as low as maybe 10x, softies and LPS in the 20x-30x range, and SPS can go as high as 100x.

IMHO, running much more through the sump than the skimmer can handle is just moving water to move water. Not terribly efficient or cost effective. I am for a max of about 10x through the sump. The lion's share of your flow in the tank should be provided by in-tank power heads of whatever sort you like.

For my SPS dominant 120DT, I started with a eheim 1262 as the return. After 4' of head pressure and a manifold for reactors I might be getting 500gph to the tank (5x+ turnover), probably a little less. I also used 4 x koralias rated at 1950gph each in tank. That gave me somewhere in the 80x range for turnover. I recently switched to 2 x Gyre 250's for a little better control and variability, as well as getting rid of the manifold and using separate pumps for them. I'm thinking of adding a couple smaller power heads in back of the rockwork just to get rid of a couple troublesome dead spots.

 

[kiMxD]

Thanks for the replies.

I can use my Jebao wave makers at 100%, but won't that be way TOOOO STRONG? I mean, using them at almost the lower setting is already quite a bit of a flow... To turn about 30x or more I'd be using around 50% of my wave maker's power...

I am just afraid of blowing everything away in my tank.

Can you guys tell me how you calculate your flow? Is my math wrong?

Thank you again!

My tank is a mix reef with LPS, SPS, live rock, sand, inverts and fish

 

[kiMxD]

I see at least two problems with your tank turnover calculation:

First, you should only use display tank volume. (actual volume not "tank size", and not include sump.)

Second, I assume that 1320 GPH is the return pumps "advertised" flow at zero head -- your actual flow would be less, even if running at max.

What is "zero head" supposed to mean?

 

[mcgyvr]

https://en.wikipedia.org/wiki/Hydraulic_head

and make the math simple.. and don't over complicate it..
The general guidelines of 30x,etc.. aren't really that scientific so no point in being scientific with trying to meet them..

You have 2 powerheads capable of 2100GPH..
So 2 x 2100 = 4200
4200/75 = 56x turnover when on 100%..
Good enough and pretty strong.. run them at less than 100% and you should still be good..
Make an assumption that if you run them at 50% you get 23x turnover.. a bit low so up them past 50%

Return pump
1320GPH /75 = 17x turnover.. = too much
But once you look at the head you have an the pumps flow chart you may find that your 1320 is really 500GPH/75 = 6x.. good enough run it at 50% and you are 3x.. Good enough..

Seriously.. don't make it complicated.. just make guesses/assumptions and you will be fine..

 

[kiMxD]

https://en.wikipedia.org/wiki/Hydraulic_head

and make the math simple.. and don't over complicate it..
The general guidelines of 30x,etc.. aren't really that scientific so no point in being scientific with trying to meet them..

You have 2 powerheads capable of 2100GPH..
So 2 x 2100 = 4200
4200/75 = 56x turnover when on 100%..
Good enough and pretty strong.. run them at less than 100% and you should still be good..
Make an assumption that if you run them at 50% you get 23x turnover.. a bit low so up them past 50%

Return pump
1320GPH /75 = 17x turnover.. = too much
But once you look at the head you have an the pumps flow chart you may find that your 1320 is really 500GPH/75 = 6x.. good enough run it at 50% and you are 3x.. Good enough..

Seriously.. don't make it complicated.. just make guesses/assumptions and you will be fine..

Thank you for your explanation, but...

If I run my wave maker at anything above 50%, it will most likely blow everything all over the place, that's the reason why I am using them at 20%, does it make sense?

To be honest, I am afraid of hurting my soft corals when using my wave makers, I am not sure how much flow is too much for them (torch, hammer, frogspawn, green star polyps, xenia, etc)... You know what I mean?

 

[Tripod1404]

Thank you for your explanation, but...

If I run my wave maker at anything above 50%, it will most likely blow everything all over the place, that's the reason why I am using them at 20%, does it make sense?

To be honest, I am afraid of hurting my soft corals when using my wave makers, I am not sure how much flow is too much for them (torch, hammer, frogspawn, green star polyps, xenia, etc)... You know what I mean?

torch, hammer, frogspawn are LPS corals. They can take good amount of flow as long as it is not direct.

 

[kiMxD]

torch, hammer, frogspawn are LPS corals. They can take good amount of flow as long as it is not direct.

Yes you're right. What about my polyps, Xenia and zoanthids? Can they tolerate high flow?

What about the fish, will they be able to sleep with such a high flow?

 

[mcgyvr]

Thank you for your explanation, but...

If I run my wave maker at anything above 50%, it will most likely blow everything all over the place, that's the reason why I am using them at 20%, does it make sense?

To be honest, I am afraid of hurting my soft corals when using my wave makers, I am not sure how much flow is too much for them (torch, hammer, frogspawn, green star polyps, xenia, etc)... You know what I mean?

Corals should move.. The ocean is a pretty violent place.. Once you've been scuba diving you know its far from calm/peaceful in many places and corals do just fine..

You just don't direct the powerhead right at them from 1ft away..
Have it blow across the front glass or upwards towards the center/top,etc.....

And yes those are LPS corals not soft corals but I understand where you are going there..

In general the PP powerheads do have a very strong directional flow straight out of the heads.. Its not too spread out at all.. Thats the biggest flaw of those.. Other powerheads may spread out the flow in a wider pattern..

Not to mention I do not believe that the output of a powerhead vs its percentage is linear..

AND.. again.. Don't over complicate it..
If 20% is looking like quite a bit of flow in your tank and detritus is being blown around and not settling and you don't see any dead spots then who cares what the calculated number is.. Its really all about a visual inspection of the flow and only using the generic flowrate recommendations as a starting point..

 

[kiMxD]

Corals should move.. The ocean is a pretty violent place.. Once you've been scuba diving you know its far from calm/peaceful in many places and corals do just fine..

You just don't direct the powerhead right at them from 1ft away..
Have it blow across the front glass or upwards towards the center/top,etc.....

And yes those are LPS corals not soft corals but I understand where you are going there..

In general the PP powerheads do have a very strong directional flow straight out of the heads.. Its not too spread out at all.. Thats the biggest flaw of those.. Other powerheads may spread out the flow in a wider pattern..

Not to mention I do not believe that the output of a powerhead vs its percentage is linear..

AND.. again.. Don't over complicate it..
If 20% is looking like quite a bit of flow in your tank and detritus is being blown around and not settling and you don't see any dead spots then who cares what the calculated number is.. Its really all about a visual inspection of the flow and only using the generic flowrate recommendations as a starting point..

Thank you man!

But I do have some dead spots that I try to clean moving the wave makers from time to time, creating different dead spots. should I lower the wave maker so I can direct it upwards? Thank you!

 

[kiMxD]

What if I put some silver tape strap in the middle of the PP wave maker? Would that spread the flow a bit more?

 

[billdogg]

Even with my system running at at least 80x the fish not only aren't bothered by it, they seem to enjoy it. My Tomini Tang likes to "surf" in the outflow from the gyres, and at feeding time, with that much rather chaotic flow, the food is all over the place, much like it would be if it were live. It seems to stimulate everyones hunt it down and eat it response.

As to your question about zero head pressure - that is the maximum output from a given pump when the inflow and outflow are at the same level - think powerhead in a bucket if you will. Head pressure is the height of the water column that the pump must push against. Assuming a "normal" setup with sump below the tank in the stand, you are looking at about 4' that the pump must push against to return the water to the tank. All pumps have a maximum head pressure after which the pump will continue to turn but no water will come out. For the pumps we use, this pressure does not hurt the pump at all, but must be taken into account when thinking about total flow. Many pumps have a fairly dramatic dropoff due to this - hence the need for "flow" pumps vs pressure rated pumps. This is especially true for those whose sumps are located in the basement underneath the tank.

hth!

 

[kiMxD]

Even with my system running at at least 80x the fish not only aren't bothered by it, they seem to enjoy it. My Tomini Tang likes to "surf" in the outflow from the gyres, and at feeding time, with that much rather chaotic flow, the food is all over the place, much like it would be if it were live. It seems to stimulate everyones hunt it down and eat it response.

As to your question about zero head pressure - that is the maximum output from a given pump when the inflow and outflow are at the same level - think powerhead in a bucket if you will. Head pressure is the height of the water column that the pump must push against. Assuming a "normal" setup with sump below the tank in the stand, you are looking at about 4' that the pump must push against to return the water to the tank. All pumps have a maximum head pressure after which the pump will continue to turn but no water will come out. For the pumps we use, this pressure does not hurt the pump at all, but must be taken into account when thinking about total flow. Many pumps have a fairly dramatic dropoff due to this - hence the need for "flow" pumps vs pressure rated pumps. This is especially true for those whose sumps are located in the basement underneath the tank.

hth!

Thanks Bill!

I've calculated my head loss and my pump should drop from 1320gph to 971gph. But I still don't use it at maximum power because it will dry out my sump before the overflow can replenish it. So I have to run it at about 70% of it's power...

I am probably turning my tank over around 6 times...

 

[billdogg]

What if I put some silver tape strap in the middle of the PP wave maker? Would that spread the flow a bit more?

NO METAL!!!!

The directional flow of most power heads is the reason I used 4 koralia PH's before I switched to the Gyres. By staggering their placement on the back glass you can get them to interact with each other in a more "random" way.

I placed them, from left to right:
1. middle of tank a couple inches from the side, angled up and in
2. just left of the center overflow about 4-5" below the surface angled up and in
3. just right of the center overflow about 4-5" below the surface angled up and in
4. middle of tank a couple inches from the side, angled up and in

Notice how all are pointed up towards the surface. This is to increase surface agitation and thereby increase the amount of dissolved oxygen in the water. As an added bonus, it tends to kick up the least amount of sand that way.

If it seems that your softies or LPS corals are getting blown around too much, try to locate them near the rocks where the flow will be dampened somewhat.

 

[billdogg]

Thanks Bill!

I've calculated my head loss and my pump should drop from 1320gph to 971gph. But I still don't use it at maximum power because it will dry out my sump before the overflow can replenish it. So I have to run it at about 70% of it's power...

I am probably turning my tank over around 6 times...

What size is your drain form the DT and what style is it? (DURSO, Bean Animal, Herbie) If it is the standard, supposedly "reef ready" drain setup with just a single 1" drain using a Durso style, then the max you will be able to put through it is ~300gph. It isn't until you switch to either of the others and use a full siphon drain that you'll get more than that.

 

[kiMxD]

NO METAL!!!!

The directional flow of most power heads is the reason I used 4 koralia PH's before I switched to the Gyres. By staggering their placement on the back glass you can get them to interact with each other in a more "random" way.

I placed them, from left to right:
1. middle of tank a couple inches from the side, angled up and in
2. just left of the center overflow about 4-5" below the surface angled up and in
3. just right of the center overflow about 4-5" below the surface angled up and in
4. middle of tank a couple inches from the side, angled up and in

Notice how all are pointed up towards the surface. This is to increase surface agitation and thereby increase the amount of dissolved oxygen in the water. As an added bonus, it tends to kick up the least amount of sand that way.

If it seems that your softies or LPS corals are getting blown around too much, try to locate them near the rocks where the flow will be dampened somewhat.

Does silver tape contains any metal on it? I thought was just the name cause it's silver color, lol...

I only have two pumps, so what about one on each side of the tank? I usually use my return pump output for surface agitation, seems to work pretty well with a T connector I have, I split the return to both sides of the tank at the surface level...

 

[kiMxD]

What size is your drain form the DT and what style is it? (DURSO, Bean Animal, Herbie) If it is the standard, supposedly "reef ready" drain setup with just a single 1" drain using a Durso style, then the max you will be able to put through it is ~300gph. It isn't until you switch to either of the others and use a full siphon drain that you'll get more than that.

Are you asking about my overflow right? If that's the question, I am using PF-800 from Eshopps.

If you're asking about my return pump, I am using a clear hose coming from my return pump all the way to my DT and then a T lock-line connector splitting the flow into two.

 

[mcgyvr]

Does silver tape contains any metal on it? I thought was just the name cause it's silver color, lol...

Do you mean duct tape?

 

[kiMxD]

Yes, I guess it could be too.