salt question

[xsdbs]

good morning everyone, i am wondering what the advantages are of using more expensive salt. what are the differences between a $10 bag of salt and a $20 bag (besides the $10 difference). also I have a question on dsb water change and cleaning. I get some light brown (diatom) on my sand top layer. I have recently restructured my tank with max's and others help from this forum from crushed coral to a dsb. the tank is doing nice. i use a python for the water change. with my cc setup i was told to plunge the tube into the cc to suck up debris and from the forum i do not think this was correct, knowing a little more about the copods. I was probably sucking them up as well. so with the sand bed should i just wave my hand gently above the sand or just barely use the phython to gently siphon off the top layer. thanks in advance for any help. (sorry for being so long winded)

 

[Fishieness]

siphoning out CC is necessary because so much debris settles in it. but it would have damaging effects on a DSB. you wont do anything but start a sandstorm and destroy your established sand bed.
for the diatoms, you can get a few different sand sifting snails (avoid the staarfish) or a type a gobie might help. but once your sandbed is established, the diatoms should go away

for the salt, IMO, there is a huge difference. many of the cheaper brands do not have the necessary trace minerals that you would need in a reef aquarium and are highly recomended in a FO such as acceptable levels of Ca and Mg.