UV water good. Green, murky water bad. Once you get it
all plumbed and wired, it's a no brainer. Lamps last
about 3 years (use a lamp until it burns out). The larger
the assembly the better the job it can do: consider that,
if you have:[*]

3600 gl water
3600 gl/hour pump rate (1 gl per second)
1 gl exposure (ie, the UV assembly holds one gallon)

Then, at most, on any Sunday, you touch the 3600 gallons
of water 24 times a day, for a grand total of only 24
seconds. With lower pump rates, and smaller UV jobs,
that'll be less. What's the big deal? Only that 24
seconds a day means it can take several days to clear
up the water, that's all. Once it gets clear (you see
the bottom) all that matters is that the UV keeps it
that way. You won't be using the UV for any purpose
but to rid yourself of that stinkin', green water.
[*] Feel free to adjust, correct, fold, spindle, & mutilate.
I only know UV is well worth it if you feed you fishies,
whales (grossed me out), or whatever else lurks in there.

--
'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`''`'`'`'`'`'`'`' `'`'`''`'`'`'`'`'`'`'
SLOTHEAD