Hi Sergey and welcome to Simply Discus. We look forward to seeing pictures of Ukranian discus! I hope they are all as nice as the one in your avatar.
I have not used UV sterilization previously so I cannot recommend a specific model. However, I would suggest the following.
1. UV does not actually kill bacteria. Scientifically, it causes cross linkages in bacterial DNA which prevents them from dividing. Thus, it can minimize the bacterial population in the water, but cannot reduce it, nor can it clear up a bacterial bloom. (Blue green algae is also a bacteria and would be similarly affected, but not green algae.)
2. Water absorbs UV light effectively, so the UV effect is minimal. The effective distance is far less in cloudy vs clear water, but it becomes virtually zero unless the UV tube is absolutely clear. Your ability to easily clean the surface of the UV tube should be a paramount consideration when choosing a UV sterilizer model.
Good luck, Willie