I want to know how many watt do i need uv sterilizer?
20-30 watt?
pump is 1800L/h
i go use 2 pipe each 3/4
i have clown loach,bala shark,black ghost knife, pleco and boesman rainbow.
On my 120g I use an AquaMedic 9w. This is rated for up to 75 - 135g tanks but when first setting it up took about 3 days to clear up my tank. It felt as if it did not have enough power to do the job quickly. Once it was establish it maintains the tank perfectly.
The next size (18w) was rated for 125g to 250g; This was the size I felt i should have got for my 120g.
So now that I am setting up my 210g with an FX5 filter I decided on the 36w with is rated for 250g-500g tanks. I feel this will be a better match for the high flow of the FX5.
I know that this did not answer your question but was just my experience.
I suggest you ignore any "rated for up to XXX gallon tank" rating on any aquarium components.
　
I’ve tinkered with many different UV units on many different set ups while working heavily with Blue Dempseys, which are known to be prone to parasitic illness. I found the formula: 1W of UV strength per 10 US gal of water, at a flow rate of 10 GPH per 1W of UV strength. This easily translates to 20.5W UV unit running at 205 GPH (actual flow rate, not ‘rated’ flow rate).
　
You could likely “get away with” an 18W UV light, but personally I would want a 20+ W UV unit. Especially if you increase the volume of the system by using a sump for filtration. Then use a canister filter or well pre-filtered powerhead to push the proper flow rate through the UV unit.
