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Flow/Turnover Volume calculations

LightingBamboozled

LightingBamboozled

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TL;DR when calculating flow/turnover per hour which volume matters? Tank Volume, Tank Capacity, Water level capacity, Actual water volume. And with a sump is it just the tank or whole system volume I should be considering?

A lot is made on fish and plant forums of turnover per hour with a lot of planted tank users swearing by 10 times volume per hour. I'm investigating an unexpected offer of a tank with sump considerably larger than my current set up and so am crash researching questions as fast as possible. I'm a little stumped on what volume I should consider for flow.

A 6'x2'x2' aquarium is nominally 680L. Take out glass width and some air gap at the top and it's more like 632L. Put in a couple of inches of substrate and you're down to 578, a few pounds of hardscape, some wood and plants and you may at an extreme get down to just 430L of water in the tank.

Assume a 42"x17"x17" sump and you take the nominal volume to more like 880 Litres actual volume around 776 Litres, actual Water Volume could be as low as 530 Litres and Tank volume is still only 430L.

So which of those numbers do I use for calculating flow?

My instinct is that actual water volume is probably the right target. The tank I'm looking at would probably have less hardscape and equipment so the tank is probably 520L and system more like 630L. It includes a nominal 5,000 l/h pump For surface movement I'd be looking at a couple of gentle wavemakers and an airstone for uplift which tells me I should be around the right ballpark, bordering on light for flow in the tank if I'm supposed to be looking at the actual water volume. But if I'm supposed to be basing it on the 880L or 776L then I might be quite under and need to consider more powerful wavemakers/powerheads.
 
Short answer: Doesnt really matter. 10x turnover is a rule of thumb, a guideline. So calculate it however you want. Most people go from external measurements even though its not actually the amount of water in the tank. If you have a big sump just add a rough amount to the total volume. Dont worry, it will be fine 😄

There is no need to add precision because there are numerous other factors like velocity of water, hardscape placement, outlet placement, etc etc that will factor in. Precision is impossible, or at least nobody else is being that precise so the rules of thumb were not meant to be used that way :thumbup:
 
Just add the gross volume of the tank and sump. For flow you might want to only consider the gross volume of the tank as mentioned. In a planted tank, flow - as in distribution of nutrients - is much more important than turnover. Prioritize flow. Doesn't matter if your turnover is 5 or 15 times if your flow is inadequate. In a densely planted tank the bulk on the biological filtration is done by the plants and the substrate. Flow! :)

Cheers,
Michael
 
I'm not looking for accuracy but 5,200 and 8,800 are very different numbers. , I could do with less than a 70% variance in one of the input numbers to the rule of thumb. Equivalent of going from 10x to 6x or 17x. The aim is to just make sure there's consistent flow throughout the tank. but for estimating that in my head and considering what I want to add in terms of powerheads/wavemakers, and therefore the extra cost to this tank I'm considering buying it matters a little.

Turnover is less of an issue, anything over 3x will be fine for what's needed in the sump.
 
Consider that 10x was originally meant for canister filters, where they usually output something closer to 50% of the specs once they have filter media and resistance in effect. The 10x figure is taking that into account, so in reality we might be talking closer to 5x. Then theres the implementation of the flow too like ive mentioned.
A wave maker will likely output much closer to its specs than a canister. I suggest going with external measurements for your tank because thats what almost everyone uses.
 
Why not tale a median value of the tank volumes you’ve provided and worse on that basis. As others have said, the key is flow, ensuring covers all parts of the tank at somewhere between 5-10x volume. I watched a George farmer video recently and he had a high tech tank that had 6x flow.
 
Hi,
I've never had a sump but I would imagine it will have an optimum through flow rate (efficiency, noise etc) so for me a 5,000 - 10,000/lph variable speed DC pump would suit.
Any additional required in tank flow can be covered with Gyres or the humble AI Nero.
Cheers!
 
For a sump located under the tank, it may be important to consider the reduction of flow due to the height difference. Some pumps lose a significant flow amount with 1m height. In canisters, this isn’t important since the system is closed and the inlet and outlet are at the same water height.

I consider this rule for filter turnover to be based on total tank volume, regardless of what’s inside. This rule should account for standard volume losses. If your tank is exceptional in some relevant way, you wouldn’t be using a rule of thumb. Don’t consider the sump volume.
 
LightingBamboozled said:
TL;DR when calculating flow/turnover per hour which volume matters? Tank Volume, Tank Capacity, Water level capacity, Actual water volume. And with a sump is it just the tank or whole system volume I should be considering?
Click to expand...
IMO disregard the sump to display tank flow figures. Turn over in the planted display tank is what matters. Use gross displacement of your display tank and go for x10 'out of the box' for a flow to aim for. Flow will always be less due to plant growth and will never be uniform.
As for meds & ferts total combined net volumes of your system will be your aim.
Good luck with your set up.
 
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