When I had ich in my tank, I turned the temperature up, added 1 teaspoon of salt for every gallon (gradually), added malachite green and did a daily gravel vac to pick up the ich tomites from the gravel surface. The ich disappeared and hasn't returned since. However I've never had fry so I'm not sure if this is as practical for them.
You can't actually treat the white spots when they are on the fish, you have to wait until they reach maturity, leave the fish and fall to the bottom. At this stage you can syphon them up before they reproduce and reattach themselves to the fish. It's not unusual for the white spots to disappear and then a day or so later, return in abundance. It just means that they've fallen off, reproduced and attached themselves again. Also, turning up the temperature speeds up the life-cycle of the ich, so if you do a daily gravel vac, it increases your chances of removing it. The ich medication should hopefully catch the ich whilst it is in its free-swimming form, but a lot of people manage to overcome ich without the use of meds.
Sorry, not sure if any of this as safe for fry, but I know it worked on my guppies.