Bryan, I'll post it here so I can find it in the future. And I have had a few inquiries so maybe this will help some folks gain a better understanding.
This is probably more info than anyone wants but I hope it will be a good read for those interested.
Lee has an excellent sticky about it which I have seen interpreted as UV is a waste of money, and I interpret as UV can be a valuable piece of equipment.
http://www.reefsanctuary.com/forums/fish-diseases-treatments/45307-uv-u-me.html
An excerpt from the above:
I would include a UV unit in a marine system that is overstocked with fishes or which is being overfed. (Both of these conditions encourages excessive proteins and bacteria in the water and also will help prevent any bloom of the bacteria). I would also definitely use a UV unit when there is less than optimal water clarity. Beyond these conditions, the use is optional. However, the downsides have to be considered.
I highlighted in red, to emphasize my point...it doesn't say the use is wasted, nor wrong, nor useless, nor anything negative...just optional. Check the sticky, the only downsides Lee talks about is heat, and expense, both of which, I can deal with.
My take on UV. This is mostly my opinion, and anecdotal from what I have read. Some is 100% fact but you should do your own research before you spend your own money. Hopefully this will give you a starting point on what to think about.
IMO UV is very misunderstood. It can have many uses, and a lot more misuses. I posted the above and the fact that I have seen posts that summarize this sticky as "it says UV is a waste of money. More of why I say it's misunderstood.
An undersized UV is probably useless. If you're not going to get a properly sized unit, spend the money somewhere else. It's not one of those situations where some is better than none, undersized is about equal to none, so don't bother.
Contrary to popular belief a large enough dosage of UV can kill almost anything including ICH. Yes a UV can/will kill some desirable things in the water column...more evidence of the "bad rap"...UV detractors say it can't kill ICH because it only kills what's in the water column and ICH spends part of it's life on the rockwork, and it will kill the good stuff like pods and such...How do they have that both ways? I reason (maybe right maybe wrong) the ICH has to attach to a host or die, therefore it will be in the water column...pods stay and even hide in the rock because that's where they are safe and where they eat. As far as good bacteria?...Start a post about the value of "live water" and see how many people tell you how little good bacteria live in the water and how the vast majority live attached to everything in the and and even the tank itself.
I don't totally disagree that ICH is difficult to eradicate, maybe not possible, I more contend lowering the population will help to keep healthy fish healthy. This is a good diagram as to why ICH is difficult
http://www.bulkreefsupply.com/store/catalog/product/gallery/id/933/image/2537/
So what is the proper size:
I refer to this chart, it lists different organisms and the dosage needed to kill them:
50 Watt (330 Gallon) Emperor Aquatics Smart HO UV "High-Output"
You'll see on that chart bacteria like Fin rot, and algae are killed at a dosage 22,000 or below, while more complex organisms like marine velvet, or marine ICH take higher dosages 105,000 and 280,000 respectively. You have to keep in mind dosage and flow go hand in hand. In theory you can achieve a very high dosage with a small unit with a long enough contact time...or a tiny unit leave the organism in it long enough and you kill it. The problem is if you have to leave the organism in the unit for a long time, by the time you kill that one, a thousand more have reproduced, why I say it's just about useless if it's undersized.
My theory, is the unit needs to deliver the dosage you want while turning the system volume about once per hour...200 gallon system the unit needs to be able to deliver the desired dosage at a flow of ~200gph. I have seen posts from people (some of them seem to have a decent grasp of UV) who say in order to get a high enough dosage you need to have a very low flow. They haven't made this connection...it is important to understand it works the other way around...you need to have a large enough output so that you can have a strong enough dosage with the flow you need. You buy the UV to support the needed flow, you don't dial back the flow to get the desired dosage.
Another key item I saw in my research was the "advertized dosage". Make sure the dosage the unit advertizes is with an older bulb and less than clear water. One of the reasons I chose the brand I did is because their dosages are at the end of the bulb's life, and with "green water"...basically the advertized dosage is under the "worst conditions" and not as some advertize under the "best conditions".
that's the great thing about RS, no dark side here !
