Water Change question and Diatoms?

So Early on when I started my 14g Biocube about 3 1/2 months ago. I jumped the gun and added to many fish too quickly and had a serious ammonia problem for a about a week until my tank fully cycled. By some miracle none of the fish were killed or even effected even when the ammonia was off the charts!! I did a 50% water change during the first week and again the second week, I've been doing 25% water changes once a week ever since. I was a bit nervous about loosing a fish when the nitrites skyrocketed but both clowns and my damsel made it. I know for sure it is fully cycled now. I didn't test the water today but it's almost always ammonia 0ppm nitrites 0ppm nitrates 5ppm. Am I changing the water to often? Is it even possible to change the water to often? I like doing the water change, so if it's okay to do it I'd like to continue especially since it's a habit now. Also, I like to know my fish have clean water to enjoy.

A second question, I seem to have a constant diatom(maybe something else?) bloom I was told by the guy at my lfs that it would go away within a month since it's now been three months I figured I'd ask if this has happened to anyone else and what you did about it. I am almost sure it's diatoms because it came during the cycle and hasn't gone away, it's just, I don't understand why or how it's lasted so long.Thanks guys!:)