I am not the expert on UV sterlizers, but I have one for my SW tank, and never hooked it up YET. (I am getting around to it!

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I wouldnt be sure fi it can rid a tank of freshwater Ich. Saltwater Ich and Freshwater Ich are two totally different things and only related by name and their appearance on fish but I wouldn't know if they are both susceptible to UV light as far as it killing them off or not.
I know in a freshwater tank, you can do some pretty easy things to avoid Ich. I learned a couple months ago that the LFS was wrong in telling me that it is always present in a fishtank, but rather it has to be brought to the tank from a host. So, if you were to quaranteen all your fish, or dont have a problem with Ich now and are not planning on stocking further, I wouldn't waste too much money on a UV, but that is just my opinion. Algea blooms in freshwater are also pretty easy to avoid so I think that is why people do not usually need to have a UV sterilizer on a FW tank. I think they also add heat to the water, which is why I am leery to put mine on my SW tank since it runs hot by itself already, and so you could have a temp problem in your tank.
For my 90 gallon tank, I was advised by a few people and resources on the internet to get a 110 watt system so I dont know if 36 watt would be good enough for your tank. You would need more intensity to filter water faster through it, so that is why I believe the wattage comes into play. Also, keep in mind that it is nearly impossible to filter all your water through it in a FW tank because you would need some considerable water flow (somewhere in the range of two to three times the volume of your tank per hour) which most FW are just not used to or can adapt to quickly.
So, sorry for the wishy washy answer...I dont have exact advice or info for you, but logically thinking, I dont know if it would really be worth your time, effort, or money.