Those charts all show the intake for those UV units starting in the sump.I am in no way an expert, but I have done a lot, and I mean a lot, of research on UV's as of lately after an unknown parasite slowly wiped out my entire tank, but that is a different thread. So I am now in the process of setting up a UV Sterilizer on my 180 gal before I start restocking. This is what I have learned after my research:
Purposes for using uv
First, Uv will kill (or damage them enough so they can not reproduce) only the things that go through the unit. Beneficial copepods and amphipods pods, which are benthic, (bottom-dwelling organisms often attached to hard surfaces such as rock, sand bed and glass), will not go through the unit and will not be harmed. However a few may get sucking in the uv. Only the free swimming ones will go through the uv. So no worries about killing off all your entire pod population. No, it will not completely eliminate all ich and other parasites from your tank but you shouldn't notice anything on your fish or have a major outbreaks that can wipe out your tank if using a properly sized uv.
- water clarity (higher flow)
- kill parasites (low flow)
Second is size of the unit. Most UV's are grossly understating the correct size you need to actually kill things. In this case going bigger is better! After my research and talking to local hobbyist that use uv, I am going with a 120 watt unit from Aqua-UV (formerly Pentair) for my 180 gal fowlr tank. If you are looking for water clarity then that is a different story and the smaller units will be fine.
Third is the flow. For water clarity faster flow is fine, but for killing parasites you will need slower flow, use the manufactures suggested flow rate for the size of the unit.
Last is placement. To be effective, 100% of the water needs to move through the uv unit. If you have it plumbed going only through your sump this will not be effeictive. Therefore placement is important. The chart @scardall linked in post #35 is a good example how to properly install a UV.
As for me, I will now run a uv 24/7.
The only difference returning the water to your display is in the efficiency of your return pumps.
1) Use the UV and return the flow to display....the gph through sump is cumulative and adds to the total gph.
2) Return the water to the return section .... you still have the same gph through sump as if you were not running a UV....the difference is a portion of the water bypasses the skimmer/refugium sections.
Lets say i run 800gph on my main pumps but run a UV at 150gph from directly behind filter socks directly to return.
Here is the total break down.
800 Gph hit filter socks.
150 gph bypasses skimmer and fuge sections and goes to return.
650gph takes the normal route through the sump, of which my skimmer processs 500gph...granted, a lot if that is recirculated with typical internal skimmers. 650 gph also goes through the chaeto bed, refugium.
No UV water gets treated twice within the sump unless your UV return comes back to the same section as your feed pump.
I am also not convinced that the manufacturers flow rates are 100% accurate.
Pentair says with a new bulb my unit can do 330gph sterilization...they say a 1 year old bulb does around 260gph. Then they say that any discoloration of the water or routine build up in the system means you need to disassemble and service or slow the flow yet again.
Since i don't actually have parasites and algae i am not sure i will always keep on schedule with much other than a yearly clean and bulb replacement. (The idea here is LOW maintenance).
No doubt i am loosing production right now at 125gph, but by years end ill bet that's about right.
Of course, if/when i do observe problerms with algae or fish behavior you can bet ill take the time to clean it and possibly add flow.
http://www.americanaquariumproducts.com/images/graphics/uvsumpflow.jpg (This link may help)
