UV light in canister filter

[Sabrina]

I recently brought a new canister filter which has a big UV light inside it, I have been researching online about the UV light and most commonly people are saying that you need to replace the UV tube every
6 months because at this age the UV light will be only working at 50% of its capacity. Is this true? And is 6 months a good time to install a new UV tube? I also read cleaning the quartz cover often is a must, how often would I need to do that? And would I also need to replace the quartz cover when I replaced the UV tube?
On one account I read that the UV light kills beneficial bacteria, and on another account I read it does not kill it, which is true?
I found the UV tube and Quartz cover replacements on Ebay for my model canister, they come in packs of 2 for only $25.. I was going to buy a pack of each item, my idea was to get the quartz covers in case while I was changing the UV tubes I broke the quartz cover.. Any help on this would be appreciated a lot :)

[Foxfire]

A UV source will generally destroy most types of bacteria and will not selectively kill only bad bacteria. That said, good bacteria live in the bio-based material in the filter and will constantly be created. So, unlikely the UV light will be 100% effective in killing all of these that escape the filter; so some good bacteria should make it into the tank. In any case, since the filter media in the canister does not see the UV source, the good bacteria there is safe. As for a replacement capsule for the canister, not a bad idea to have a spare if one thinks they will break the existing one. I've had mine for tens years and never once considered that a concern. Changing the bulbs is necessary - the mfg likely offers a time period. Can't go wrong if one replaces every 6 months but again, check the manual for the unit.

[Paul Sabucchi]

The effectiveness of a UV unit depends greatly on how it is employed, mostly it depends on how long the micro-organisms are exposed to the UV light and how strong this is. So how many Watts is the lamp and what is the flowrate of the filter? In most cases these UV fitted inside canister filters are effective killing unicellular algae but not enough to be bactericidal. As stated above even if they are powerful enough they will only kill what goes through the unit and not what does not, be it bacteria (good ones in the media or bad ones in the slime that can coat the tank/plants/decor) or algae like green string or black brush algae (but it may have some partial effect on these if they produce free floating spores)

[jawfish]

Yes its true, you need to replace the tubes every six months as the output of the tubes has diminished.

Yes it will kill any bacteria expose to it at the proper exposure. hence the reason to change the tube and clean the quartz sleeve.
Will it kill beneficial bacteria, yes if its expose... I would suspect that the filter media basket a shielded from the UV light hence no worries.

Cheers

Fred