UV flow for optimal effect

Fiziksgeek · May 21, 2023

Hey all,

I am thinking of adding UV to my tank. You can see my build thread, but the main display is a 72x36x26 peninsula, the total systems volume is around 400 gallons. I have had a small issue with cyano (beat it), currently fighting (and winning) against some bryopsis. Looking to increase my fish load, so ya never know when ich might rear its ugly head. Lots of reasons why UV might be a good idea, thinking more of a preventative than anything right now.

I could add the UV to the return line form the remote sump OR I could add it to one of my closed loops. Either would require minor plumbing work.

My understanding is that when trying to battle dynos or algae, you want high flow, but when working on things like ich, you want lower flow. I have dual closed loops running Vectra L2s, I have been running reef crest during the day, lagoon mode at night. What if I were to just use a fixed speed, higher flow for 12 hours, lower flow for 12 hours, so over a 24 hours cycle I would get high and low flow. Seems like it would be the best of both worlds? Anyone run a UV like this?

Reefing Madness · May 25, 2023

Gundy · May 25, 2023

It’s an interesting idea. Assuming your UV is sized correctly - even better, oversized, you will probably get the best results from choosing one flow speed for a specific purpose. Algae reproduces very fast but very susceptible to UV at a fast flow rate. Slowing the flow down will greatly reduce the effectiveness of killing the Algae but be more effective in killing Protozoa which you may or may not need. In other words this concept will probably do a poor job at keep your water clear and killing Protozoa because when you slow the flow down, the algae can reproduce faster than you are killing it.

Every tank is different and depending on what your tank needs from the UV, it might work. Especially for killing algae if your algae problem is not that bad. By significantly over sizing your UV, like a 150 watt Pentair unit, you can set the flow to do both. This UV is 6 feet long and nearly 6 inches wide and is a monster, being probably 3 times the size needed. The flow will be probably slower than you need for Protozoa control but fast enough for algae control. This is what I will be doing for my upcoming 400 gallon system I am planing.

UV’s are a controversial topic. Many swear by them, many don’t believe in them and many haven’t done any research to form an opinion.

Fiziksgeek · May 26, 2023

Gundy said:
It’s an interesting idea. Assuming your UV is sized correctly - even better, oversized, you will probably get the best results from choosing one flow speed for a specific purpose. Algae reproduces very fast but very susceptible to UV at a fast flow rate. Slowing the flow down will greatly reduce the effectiveness of killing the Algae but be more effective in killing Protozoa which you may or may not need. In other words this concept will probably do a poor job at keep your water clear and killing Protozoa because when you slow the flow down, the algae can reproduce faster than you are killing it.

Every tank is different and depending on what your tank needs from the UV, it might work. Especially for killing algae if your algae problem is not that bad. By significantly over sizing your UV, like a 150 watt Pentair unit, you can set the flow to do both. This UV is 6 feet long and nearly 6 inches wide and is a monster, being probably 3 times the size needed. The flow will be probably slower than you need for Protozoa control but fast enough for algae control. This is what I will be doing for my upcoming 400 gallon system I am planing.

UV’s are a controversial topic. Many swear by them, many don’t believe in them and many haven’t done any research to form an opinion.

Thanks for the response. I've been doing a lot of reading on the current thoughts trends, and you are right, some people wont run a tank without, some wont run a tank with. I just watched the youtube video of Randy from BRS and Lou Ekus from Tropic Marine (who I have met before). Randy swears by them, Lou says never, unless you are trying to address a specific problem.

Initially I was thinking like an 80 watt unit. If I am reading their specs right, the E80s, which is a single lamp, 80w, for 30MJ/CM2 you want 2700 gpm of flow and for 180MJ/CM2 you want 420 gph. My closed loops each have a Vectra L2 which would seem to be the right sized pump for delivering that flow.

If I were to go up to the 120, it would be 3840 and 400 gph respectively, and the 150 would require 6000 and 1000 gph respectively. So even the 120 seems out of reach for my L2, let alone the 150! Only real option there would be to combine my 2 closed loops into a single closed loop with a single large pump, probably a big Abyzz or Red Dragon..$$$$. And then the issue would be trying to plumb a nearly 6ft long UV under my 6ft tank!

I am running about 1000 gph through the return from my remote sump, and obviously, I would like to keep the return flow constant so that my overflow stays quiet. definitely dont want to have to adjust the gate valve constantly.

I guess I will let the idea stew for a bit....

Gundy · May 27, 2023

Putting UV’s under your tank in a cabinet is sometimes a problem. In regards to the UV size, the idea of upsizing is not to follow the exact recommendation from the manufacturer but slowing the flow or increasing contact time for Protozoa control. That’s why a lot of UV users say by the biggest one you can fit under your tank. If you could fit the 120 under your tank, you could keep a similar flow as the 80 but have a significantly powerful UV which will have a much greater kill rate. This idea of over sizing really comes into play with Protozoa control. If you get an Ick outbreak in your tank and have, say twice the needed exposure time that is recommended, you will kill ( or sterilize ) the Ick twice as fast. Thus, perhaps even preventing an outbreak from starting.

I saw a video of a guy who hooked up a 150 watt UV- way oversized for the tank, for a tank that got a bad ick outbreak. Within 2 weeks the spots were all gone and all fish doing well. This forum is full experiences just like this. For me, I feel oversizing the UV is the best option, even if it means not running it 24/7 if it’s not needed. With UV’s it’s always better to be oversized than undersized. Just my .02 cents.

Fiziksgeek · May 29, 2023

Gundy said:
Putting UV’s under your tank in a cabinet is sometimes a problem. In regards to the UV size, the idea of upsizing is not to follow the exact recommendation from the manufacturer but slowing the flow or increasing contact time for Protozoa control. That’s why a lot of UV users say by the biggest one you can fit under your tank. If you could fit the 120 under your tank, you could keep a similar flow as the 80 but have a significantly powerful UV which will have a much greater kill rate. This idea of over sizing really comes into play with Protozoa control. If you get an Ick outbreak in your tank and have, say twice the needed exposure time that is recommended, you will kill ( or sterilize ) the Ick twice as fast. Thus, perhaps even preventing an outbreak from starting.

I saw a video of a guy who hooked up a 150 watt UV- way oversized for the tank, for a tank that got a bad ick outbreak. Within 2 weeks the spots were all gone and all fish doing well. This forum is full experiences just like this. For me, I feel oversizing the UV is the best option, even if it means not running it 24/7 if it’s not needed. With UV’s it’s always better to be oversized than undersized. Just my .02 cents.

In the grand scheme of things, another $1-1.5K into my tank for a big honking UV isn't going to move the overall budget much. I never want to be wasteful, but its just money! Mounting location is going to be the biggest issue. with a constant 1000gph flow, what size UV would you recommend? The 120 watt?