UV will not kill/weaken BB as long as it’s AFTER the filter unit. I.e. attached to the outflow after the water has passed through the main filter media
But eventually the water comes from inflow, passes through the filter media before exiting through the outflow, carrying beneficial bacteria in the whole process? Unless the filter can distinguish between the beneficial and harmful bacteria and avoid letting beneficial bacteria pass through the filter media.
UV kills all - but there are more than enough bacteria in filter and the substrate and on the surfaces to ensure that a healthy population is maintained, bacteria in the water column will be kept down to low numbers.
UV only weakens what passes through it. If the water passes through your media first, then it colonises there, and the rest gets exposed to UV light on the way out. This is why its best to have the UV AFTER the filtration.
Thank you
I run a Fluval 407 with an in-inline Fluval UV on the return to the tank. I am not sure Fluval does sell filters with integrated UVs. Many UV systems built-in to the filter are a bit of pain because UV bulbs need to be changed, and over time plastic clips, etc., perish and break, I run a fairly effective UV combined filter in my goldfish pond, but next time the bulb blows it is a new filter for me, the passage of time in a watery world has made maintenance now too difficult. It works a treat to stop green water in the Spring. My UV on my main tank works a treat to protect my surprisingly sensitive black mollies. A friend now uses UV to protect his Discus, my suggestion and has had no disease issues since. Most fish diseases are parasites of some sort and have a free swimming stage, knocked out, or, massively reduced in numbers by UV. Here in the UK, All Ponds Solutions sells pretty effective smallish combined internal filter UVs for aquariums, the bulb is easily changed for at least a few years before the inevitable brittle plastic issue. The filter bit, however, is very modest and needs to be cleaned regularly. I hope that clarifies things, pun intended! Happy Christmas to all.
See please my little post to Bradders above.
Regarding beneficial bacteria, it doesn't matter if the UV filter is on the inlet or outlet of the filter. Traditionally the UV unit is positioned after the filtration to reduce the maintenance and increase its performance. You want crystal clear water to reach the UV, so you don't have to clean it, and the UV light can kill stuff more efficiently.
In a new setup, you won't want to pass the water through the UV before getting to the filter. The UV light does not discriminate against what it weakens - BB or pathogen.
I can confirm that is the case. I have the 207 on my tank and there is definitely not an integrated UV. I can’t imagine where one would fit; it’s only a wee filter.
It's exactly the same, doesn't matter where you put it, before or after.
In a new setup, you want to ensure all the column water passes over the biomedia so bacteria can colonise efficiently. If you place a UV before this, it weakens (or mutates) what gets to the biomedia. Some beneficial bacteria require a surface, and once they cling to the biomedia, they won't (on the whole) pass through the UV light again, thus limiting the loop you describe above.
