Why not just use a good SPS salt?
Of course you should use good salt. I am really not aware of too many bad ones though really.
If you do weekly water changes you shouldn't need to dose - or am I wrong?
Only if this was the fish only forum would you be right.
If your corals use up the Alk and Ca enough to drop your levels too low in the first 12 hours, even after that water change with "good salt", that would mean that your corals are pretty much dying the rest of the week until the next water change.
Making your water livable for your SPS once a week for 12 hours is not really an option.
You have to test enough to know what your parameters are all the time. That way you can add Alk and Ca back to your water at the same rate it is being used up. As close as you can anyway. This is way you keep your parameters
STABLE.
You don't want to dose your Alk up to 12 on Monday and then dose it again on Wednesday when it drops back down to 6.
You don't want to dose your Alk up to 10 everyday at noon and have it drop back down to 7 by the next day at noon.
For SPS this will not likely work out to well.
What are the ideal perimeters for SPS?
There are many different ideas about what "ideal" is.
"Ideal" is
NOT chasing a certain number. It is keeping whatever number from changing too much throughout the day and night.
For myself personally I have seem the have the best results with:
Alk 8 - 9
Ca 400 - 480
Mg 1300 - 1450
