Lawrence,
When I first got the Achilles he got ich within 24 hours of going in the tank. But after a week he cleared up. In the past month I've only spotted ich on him 1 or 2 times.
Amazingly with all the equipment outside, and changing weather in the past month some days the temperature drifts as much as 5 degrees. But I tracked the temperature swings with the days the Achilles had ich and they were not the days with the biggest swings. Or days following the bigger swings.
On Friday I replaced the ballast, bulbs and cleaned he sleeves of my UV to get it up and running again. I run a very slow flow rate through a dual chambered 80w UV. Maybe only 350gph.
If you come across more of the masked angelfish give me a buzz. I might be interested in picking up a small one.
Dave