Why are flow rates for UV sterilizers so low?

[Auqaman]

I'm looking into getting a UV sterilizer for my 65 gallon tank. I'll be hooking the inlet of the sterilizer to the discharge of the return pump, then hooking the discharge of the sterilizer to the pipe that goes back to the display tank. For my tank (reefer 250) the recommended flow rate is 660GPH, so that's a flow rate I like to maintain.
I'm thinking all I need is a 15W or 18W sterilizer should be plenty. But their flow rates are around the 200GPH to 250GPH. The only way I can achieve a 660GPH flow rate is if I get something ridiculous like 40W. Do I really need to buy a 40W? Or can I get away with a 18W and go higher then their recommend flow rate?

 

[najer]

I used to run industrial sized units, this comes up quite often, there are different UV units, some are just water claifiers and some are useful UV, the lower flow rate will be dwell time ie the amount of time exposed to the uv, I don't know all the science on this but basically if it is cheap it is a water clarifier and not a fish helpful UV.

 

[Auqaman]

Thank. I was looking into getting a Aqua ultraviolet light.

Ultraviolet Water Purification System - Ultraviolet Light Sanitizer

We have the best and latest technology to safely purify the water you use. Contact Aqua Ultraviolet to see the latest in ultraviolet light water purification.

aquaultraviolet.com

I'm thinking the 15W should be fine but the flow rate is so low on it and I don't want to dial down the return pump

 

[piranhaman00]

What is the sterilizer for? If you are looking to clarify the water (kill algae, bacteria, one celled org.) then you can easily do 660 gph on either of those. If you are trying to kill parasites then you need to be around the 200gph. 660gph will turn you over 10x/hr which should be adequate for clarifying.

Contrary to what I just said, I am turning my tank over about 2x an hour and all returns feed through UVs. My water is very clear with that low of turn over.

Who recommends 660gph for that tank? That is a 10x turnover which seems like a lot.

 

[malacoda]

If you feed it off of a tee in the return line after the return pump, you could use a gate valve to control the flow through the UV without having to change the return pump flow rate.

As side note though, many consider best practice to be running on it's own line with its own pump straight from, and back into, the DT.

 

[Auqaman]

If you feed it off of a tee in the return line after the return pump, you could use a gate valve to control the flow through the UV without having to change the return pump flow rate.

As side note though, many consider best practice to be running on it's own line with its own pump straight from, and back into, the DT.

Never thought of that. Just buy a smaller pump dedicated for the sterilizer. Makes so much sense. Thanks

 

[Auqaman]

What is the sterilizer for? If you are looking to clarify the water (kill algae, bacteria, one celled org.) then you can easily do 660 gph on either of those. If you are trying to kill parasites then you need to be around the 200gph. 660gph will turn you over 10x/hr which should be adequate for clarifying.

Contrary to what I just said, I am turning my tank over about 2x an hour and all returns feed through UVs. My water is very clear with that low of turn over.

Who recommends 660gph for that tank? That is a 10x turnover which seems like a lot.

That’s the recommended flow rate off Red Sea website

 

[trmiv]

Keep in m

That’s the recommended flow rate off Red Sea website

keep in mind the recommended rates are at zero head pressure. They are telling you to use a pump rated at 660gph not to actually have 660gph going into the tank. After head loss your flow is significantly less than 660, especially with the restrictive plumbing Red Sea uses.

 

[ca1ore]

You’re confusing two different things. Recommended flow rate is the recommended flow rate. Whether a particular pump can achieve that depends on both head and friction losses.

 

[trmiv]

You’re confusing two different things. Recommended flow rate is the recommended flow rate. Whether a particular pump can achieve that depends on both head and friction losses.

No, that is directly from Kevin Davies from Red Sea on the Red Sea group on Facebook. Their pump recommendations are at zero head.

 

[lefkonj]

The flow rate through a UV system is all about what you are trying to nuke. Flow rate X is good for algae, Flow Rate Y bacteria, Flow Rate Z single cell organisms. I would imagine you wouldn't want this plumber into your return line

 

[Larry L]

It looks like the pump situation has been sorted out, but going back to the original question in the title: UV sterilizer flow rates are low because they are all about contact time - the UV radiation has to penetrate the DNA of the bacteria or algae or dinos or whatever to eventually kill it or prevent it from reproducing. Imagine the UV radiation coming from the bulb is the flame on your stove. You could wave your hand through the flame quickly, all day long, and suffer basically no damage, but go slow enough and you get burned.