saltwater and cleansing

Question
Hi i am mike and i have a my saltwater fish tank for about 4 months and hadnt had any problems until now.  My tank is 45 gallons and have live rock in it and some other non live products.  I had a clownfish, 2 damsels, a blenny, and 2 angels in it one of my angels died without any signs and two days later another angel died following the blenny I only have 3 fish left and five crabs and this morning i noticed something growing on the fake decorations and around the glass it looks like small white particles growing almost like sand and its everywhere i do not know what this means and i am going to change my water but would like to know if i am doing something wrong

Answer
Hello Mike,

can you please tell me a bit more about yoru tank/system?  What type of filters do you have?  How often do you cleanthem?  Hat are your water peramters?  How often do you test the water?  How much water do you evaporate each day, and how often do you do water changes?  and where do you get ht e water???

thanks, and i lood forward to eharing your replies

bill