White spot is caused by Ich. Be careful, we're talking about little white spots, not blobs. If you see tiny white pinhead spots then we're on the same subject. It's Ich and it's treated with Malachite and Formalin .. sometimes salt will also cure this parasite . This salt can be in a form of a salt bath and can also be beneficial to salt the actual pond at a rate of 5% (1/2 ounce per gallon)

But if after examination of a scrape under the microscope - you find that it is a heavy infestation, then I would suggest that you first of all switch of the Ultra Violet Light, and treat the entire pond as Ich is very infectious - do not switch off the pumps or isolate the filter system as this may contain the parasite and then when you put your filtration system back into service, bingo ... you have another outbreak ...

One treatment is all that is usually required ..  but keep a check ...