Well water. That's most likely your problem. Pollution contamination. Phosphates and no telling what else. Maybe the sediment filter isn't taking out all the bad stuff, and the carbon can only do so much. That would cause the hair algae to keep going. When you're doing water changes you're probably adding a bunch of crap to the water, instead of removing it. This is why RO water is THE ONLY way to be absolutely sure you get PURE water.
You should take a sample of your water to a LFS and have it tested for everything. You should also have the TDS (total disolved solids) checked. TDS of any water you add to your tank should be at least under 10 TDS, preferably 1.
As the old saying goes, anything worth doing, is worth doing RIGHT. Why spend the money on beautiful corals and then go cheap on the maintenance?