I have a 56 gallon reef tank and I am using tap water which measures 243 ppm on a TDS meter I purchased. Is that too high to use with a salt mix? I seem to get a film on top of the water a lot and fear the tap water may be causing it. I am probably going to purchase an RO. I do have an in-line filter system on my water main (charcoal and sedement) which helps the water quality a bit but I do fear it is not enough and may be the cause of my algae issues in my tank. What is a good number for tap water prior to adding reef salt?