Hello everyone

i am a bit confused with this topic. we say tank water changeover minimum 4 tiimes an hour. uv sterilisers require certain low flows for efficient sterilisation. for example i bought an external filter which came with a recommended uv from the same manufacturer. the filter flow is 700-1200L/hr where the recomended uv flow was 100-150L/hr. all i can imagine is that there is a loop in the outflow line bypassing through the uv with a controlled lower flow..is this right?

the other option is to buy a ridiculously large uv. in my case what i find is 36W uv systems for my 120L tank. doesnt sound right

help please

If the UV is internal to the filter and the water exposed to the UV is in the same flow as the water exiting the filter and the flow of the filter far exceeds the recommended flow based of the wattage the UV is, then the setup wouldn't make sense. However, most people want their UVs to fight green water which didn't make too much sense to me, since green water seems to be the rare occurence - at least on here. I think the exposure time needed for a UV is based on it being effective against parasites/protozoa in your tank. It is still probably effective against combating green water.

There is more than one option for most UV models though. Back when I was running HOB filters on my 75g I used a UV that I pumped water through using a powerhead. I have two of those 36W units you mention.

so i guess with the powerhead you basically completely separated the flow from the filter and the uv. thats what i think i will do too. the setup is for pedicure fish spas so im more concerned with bacteria and parasites myself. found a uv by coralife which seems to work well with high flows cos of its internal design and exposure times.

thanks for help!

With the powerhead option you just get one that flows the rate you want or get one that is adjustable. The only down side is getting the tubing you need and having more stuff hang off the back of your tank.

You want to match the flow rate through the UV. UV works on contact time. If it can contact an organism for 3-5 seconds it can kill it. If it rams through and only sees the UV for less than a second, it will no do anything. Parasites such as ich need a much longer contact time. That is why flow rates are usually low.

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