Spiral path UV sterilizers vs. direct ones - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 06-25-2020, 06:04 AM Thread Starter
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Spiral path UV sterilizers vs. direct ones

Coralife Twist-series UV sterilizers (https://www.coralifeproducts.com/pro...t-sterilizers/) claim that they differ from "conventional" ones in that they force the water to take a spiral path around the UV bulb, thus increasing the exposure time.

EHEIM with their "reeflex" series (https://www.eheim.com/en_GB/products...izer/reeflexuv) seem to take the opposite approach: they differ from "conventional" ones by relying on straight flow and claim that they provide better sterilization ("...effectiveness is 1.8 times greater") by doing that.

Go figure... Clearly, most of this is marketing mumbo-jumbo, but still: does anyone have any experience with these EHEIMs? I remember that general consensus here was that "straight flow" sterilizers are typically inefficient due to insufficient UV exposure time. But here you have it, and it is no one else but EHEIM itself.

I personally use one of Coralife units inline with my canister filter. And I do notice that it is restrictive. Of course, an obvious solution would be to give the sterilizer its own separate loop. But still, I'm wondering about those EHEIMs...
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post #2 of 6 (permalink) Old 06-25-2020, 06:30 PM
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UV sterilizers work by one metric and one metric alone, contact time. Whether the thing is twisted, straight, curved, S-shape, whatever is irrelevant. Too much contact time and you kill everything including the good stuff and too little contact time and you don't kill anything.

This is why UV sterilizers need to be on a manifold where you control the flow independently from the main return. If you want a UV unit there is only 1 brand to look at, Aqua UV. They are the industry standard and not overpriced aquarium branded crap.
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post #3 of 6 (permalink) Old 06-26-2020, 04:10 AM Thread Starter
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Originally Posted by gus6464 View Post
UV sterilizers work by one metric and one metric alone, contact time. Whether the thing is twisted, straight, curved, S-shape, whatever is irrelevant. Too much contact time and you kill everything including the good stuff and too little contact time and you don't kill anything.
This does not explain much, considering that we are dealing with a recirculated system. Anyone who understands the issue would immediately ask: is contact time cumulative?

Let's say that a restrictive UV sterilizer (e.g. Coralife) makes the recirculation rate 2x slower, but provides 2x longer contact time (per cycle). Meanwhile, a straight-flow UV sterilizer (e.g. EHEIM) keeps the recirculation rate unchanged (1x), but has shorter contact time (1x, per cycle).

The cumulative contact time is exactly the same in both systems. What about the sterilization efficiency? Is it the same as well?
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post #4 of 6 (permalink) Old 06-26-2020, 09:04 AM
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Flow rate and turnover rate/contact time are inversely proportional so the dose is always the same. If you reduce flow rate you treat less water.

There are studies of recirculating systems used in food processing where pathogen inactivation is actually inferior at the lowest flow rates but flow rates above a certain rate perform the same. I suspect it's because if the water receives a dose greater than that required to inactivate a microorganism you are not getting any additional benefit while treating less water volume.

One of the most prevalent myths in this hobby is that slow is the only way to go with UV.
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post #5 of 6 (permalink) Old 06-26-2020, 03:24 PM
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Originally Posted by DiscusStu View Post
Flow rate and turnover rate/contact time are inversely proportional so the dose is always the same. If you reduce flow rate you treat less water.

There are studies of recirculating systems used in food processing where pathogen inactivation is actually inferior at the lowest flow rates but flow rates above a certain rate perform the same. I suspect it's because if the water receives a dose greater than that required to inactivate a microorganism you are not getting any additional benefit while treating less water volume.

One of the most prevalent myths in this hobby is that slow is the only way to go with UV.
Going slow or fast is neither a myth. In a reef tank if your flow is too low through the UV contact time increases and you kill all the plankton in the water column that corals feed on. A kill rate of 30,000-45,000 w/cm for example is what's recommended in that scenario. In fact, most actually run a fast flow rate in these tanks.

Aqua UV also recommends 30,000 w/cm in a freshwater tank as well. If you are using an 8 watt bulb that puts you at ~640GPH which is not a slow flow rate.

All in all though in a planted tank the size and flow rate of UV is nowhere near as important as a reef tank. An 8 watt unit can pretty much cover you up to a 200g tank whereas a reef tank would need a 25w unit for a tank that size.
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post #6 of 6 (permalink) Old 06-26-2020, 04:27 PM
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Originally Posted by gus6464 View Post
Going slow or fast is neither a myth. In a reef tank if your flow is too low through the UV contact time increases and you kill all the plankton in the water column that corals feed on. A kill rate of 30,000-45,000 w/cm for example is what's recommended in that scenario. In fact, most actually run a fast flow rate in these tanks.

Aqua UV also recommends 30,000 w/cm in a freshwater tank as well. If you are using an 8 watt bulb that puts you at ~640GPH which is not a slow flow rate.

All in all though in a planted tank the size and flow rate of UV is nowhere near as important as a reef tank. An 8 watt unit can pretty much cover you up to a 200g tank whereas a reef tank would need a 25w unit for a tank that size.
That is exactly the myth for the reasons that AndreyT and I elucidate.
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