I wouldn't say performing a water change every 3-4 days is over-cleaning the tank. I do the same and have done for years with no problems. I have heard many people say you can over-clean a tank, but i don't agree. The only time this would apply IMO is if you are using the substrate as a biological filetr. Why else would you need dirt in the tank?
IMO the more water changes the better. Well done Looby Loo, not many hobbyists are so enthusiastic.
With regard to the whitespot, it sounds like it may have been stress induced from what you say, in which case just treat it and hopefully it won't rear it's ugly head again.
Also, i doubt it will be the temperature fluctuations causing the whitespot unless your water changes are very substantial. How much water do you change at any one time?
BTT