White spot is always due to stress. Stress is caused by a few factors:
1. High nitrate/nitrite -- Fish cannot breathe properly when these levels are high. Remedy: Add nitrate/nitrite removal. May take a few days. Make sure you have ceremic rings in the filter to cultivate good bacterial that breakes down nitrate. Purchase some bacterial product and add it into the filter according to instruction.
2. Temperature drop too quickly and drastically. Remedy: Switch on the lights for a longer time. How long? -- depends on your tank and lights. Distance between them, air ciculation in your house, windy etc... Need your personal experience. At 29 degrees, white spot should disappear.
In my opinion, medication hardly works because it will not solve the root of the problem. For quick remedy, prchasue reef water and change 50% of the water in a few intervals. Repeat this until the nitrate level drop.
When recover, must take care of flter, circulation and feeding. Nitrate always shoot up in a small tank.
Hope my experience helps.