Three part question. ???

I have three different questions about my new saltwater tank. The first question is if I can top off evaporated water with dechlorinated freshwater. I understand that salt does not evaporate so you shouldn't top it off with more saltwater. I also know that I should use saltwater when doing a water change. Am I doing this right?

Next question: My tank is about two weeks old, and there is a light broun algae-like substace growing everywhere. It spread over the live rock and is dusting the sand. It looks normal and I am just wondering if this is a normal part of the cycling process. Also, there are a few very small spots of purple growing on the rock. It isn't really anything more than color on the rock. What is this?

Last question: I turned off the powerheads for a few mins yesterday to work on some stuff and noticed some very small bubbles coming up from the sand. They were very very small and just creeped up the the surface of the water. Is this normal? What causes this?

Thanks for all your help guys! Sorry for the long post, I'm just getting really into this hobby and I want to know it all! ;D

 

For top off you should be using freshwater (Ro/Di water). It is recommended that you do not use tap water as it is high in certain nutrients that fuel algaes and things you do not want in your tank.

The brown dusting of algae is a normal part of cycling and is most likely diatoms. The small purple spots are coralline algae and will continue to spread as the tank ages, it is a calcium based algae.

The bubbles being released from the sand are also common and are created from the bacteria that reside in your sand bed.

 

+1 that about sums it up.