Someone Explain Minimum Flow for UV

bevo5 · Feb 13, 2017

I've got a 40watt UV for my 200g and I wanted to turn it up a bit to help sort out a (very minor) algae issue. I've got an EHEIM pump that I can turn from 200-700 GPH I believe.

The minimum water movement for algae on this unit is 900 gph.

I guess I don't understand why it matters. Wouldn't more time in the tube just maximize the chances it kills whatever is in it?

The only reason I can think of that would matter is thats the water turnover rate needed to be useful in attacking algae in the water. Is that really it?

Pola0502ds · Feb 14, 2017

This is not my answer to your question but it may be because there is a fine line between killing algae and killing organisms like phyto or zoo plankton. The good stuff you want to keep in your tank.

Harry Muscle · Feb 14, 2017

I've always wondered the same thing. My personal best guess is that you need a certain amount of flow to prevent debris from settling in the unit ... but I'm not really buying that explanation.

Thanks,
Harry

bevo5 · Feb 15, 2017

Interesting - the thing is they want you to set it super low for killing things like ich. Like 200gph. So some of those reasons don't necessarily work with that.

stunreefer · Feb 15, 2017

bevo5 said:
The minimum water movement for algae on this unit is 900 gph.

This is probably the maximum amount of flow through the unit to kill off algae.

U/V manufacturer's list max flow rates to sterilize various organisms.

Algae and bacteria are fairly simple organisms, so can pass through a UV pretty quick and still be affected. Whereas parasites are a more complex organism and require a higher contact time (slower flow) in the chamber to be affected.

What U/V do you have?

Pola0502ds said:
This is not my answer to your question but it may be because there is a fine line between killing algae and killing organisms like phyto or zoo plankton. The good stuff you want to keep in your tank.

There' no reason to be worried abut a U/V killing "good stuff" in a reef. Phytoplankton and zooplankton do not grow to significant numbers in small reef aquaria that hobbyists keep (less utilizing a phyto reactor, but that's another animal altogether).

Some claim that they'll kill pods as well, which they might, but I have never seen a pod look good after being sucked through a return pump in the sump and shot out from the return line. And once they do, corals and fishes make quick work of them while floating in the water column.

Pola0502ds · Feb 15, 2017

I had got some live mysis shrimp and put them in the fug section of my sump. I never put them in the DT tank but i have hundreds roaming around now. The only way they made it to the DT is by going through the return pump and it didnt kill or damage them. Well maybe some but a TON made it through.

stunreefer · Feb 17, 2017

Awesome! Live mysis can be a great addition to a reef system

However, you could just add some to the display after purchasing too. There's plenty of places for them to grow and spawn in most displays. Larvae likely have an easier time getting up to the display (via return pump) than older organisms, which is likely why they spread in your system.

Suffice to say the benefits of U/V far outweigh the drawbacks. And if you're not looking for parasite control, just waterborne algae control and added water clarity, then a lower intensity can be used and the larvae would transfer up to display unscathed.

Pola0502ds · Feb 18, 2017

I actually have a empire 25watt UV that I have never setup yet because I don't have the room. It's massive! i will though

FishGuyBri · Feb 18, 2017

The flow is maximum- has to do with how much time the water that's in the UV unit needs to have contact with the UV light. It's the same for UV sterilization in a hospital, for example. Some hospitals use UV sterilization to clean rooms... many don't know this because you cannot be present while the room is sterilized. The room must be exposed for a certain amount of time in order to work. Increasing the flow reduces that time from the already low fraction of a second of exposure. UV works my disrupting the cellular division process and preventing certain functions of an organism, but is not instantaneous. Just look at humans- we can be sterilized and killed by radiation. X ray techs can only be exposed to x rays so many times until there's a problem.