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re: UV light effective to prevent algae growth

chong wan-ton asks about u.v. in planted tanks. We have an 8-watt u.v.
between our canister filter and the spraybar return (we got it at setup
time before learning that most folks don't use one). Of all our initial
algae types, green water was never among them. When we tried turning it off
a few times cloudiness (bacterial bloom) arose. That said, a u.v. isn't
really necessary for planted tanks. Free-floating algae (green water) can
be treated at the source (nutrient imbalance) and bacterial blooms clear up
in time. A u.v. will not help at all with other (anchored) types of algae.
In any case a small unit should be plenty for this purpose for most tanks
if you want one (Tetra has a new small 5-watt unit). 

Note that these units kill a few species of pathogens, but not most at
these power levels. See P. Escobal's "Aquatic Systems Engineering" for an
excellent technical discussion about sizing units and dosages for specific
pathogens. Note that he deals with "one-through" systems, whereas our water
recycles continuously. With regard to fish, a u.v. unit is no substitute
for a quarantine tank. However, if you can't solve your green water problem
(e.g. with phosphate control), a u.v. is one effective way of dealing with
it. A search in our archives should turn up more information and other views.

Jared Weinberger                    jweinberger at knology_net  
______    http://www.knology.net/~jweinberger/     ________