I have a fish r fun UV and how can I put this politely, there not that great, having said that they do seem to work but for your application you will need a far higher flow rate.

First off what is in the sump do you have a refugium or something like that?

If you do you do not want the UV on the return from the sump as it will kill all the planktonic life the refugium is producing before it gets to the tank.

However if you only have all the equipment in the sump I would suggest you set up a dedicated loop for the UV that takes water from the sump and returns it to the sump this will reduce plumbing in the main tank.

Sterilizer wise go for the TMC V2vecton its pretty much the best on the market and at a reasonable price.

If you do have a refugium in the sump what about treating the water as it goes into the sump. You would need to check the flow rate of the over flow and again may need to T is off you certainly would need to be able to shut off the overflow for maintenance. This may be the cheapest way of doing it as you would not need a pump to run it.

A picture of the sump and all the gubbins might be helpful but yu must establish flow rates in order to get the most suitable sterilizer.

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Alan

Thweeerp!