Sorry Redeye I was speaking in tongues again, lol. Most of my water is now about 4 years old, with few hundred gallons of new. On blending salt mixes, that is probably not the best idea, their have been to many case where folks have had real problems when doing this, it might work between these two salt mixes but I wouldn't try it. If your tank has a lot of calcifing corals you are going to take a hit on your alk, cal and mag no matter what salt you use. If you use a salt that is has high levels like oceanic you will end up skewing your water chemistry as the mag will effect both the cal and alk. It will be a lot harder to get these elements down to the proper balanced levels. Mag percipatates real slowly.
I would suggest going with the salt mix that is a little lower in the elements, then just rely on kalk or a reactor to keep the over all cal and alk in balance and where it needs to be. Add the Mag as a separate additive when needed. Easier to work up then down
Disclaimer of Water changes LOL: so this doesn't give anyone the wrong idea or create a fuss. I have a lot of equipment (ozone, carbon, uv, big skimmer and the use of a sock from time to time) that keeps my water clean and processed. On the replenishing of elements I dose 10 gallons of kalk a day and run a large reactor 24/7. IMHO I do not like any ASW mix as they are all skewed and out of balance and come from low end raw materials containing far to many impurities. I do not suggest my method for any reefer or aquarium keeper that does not have simular equipment or ability to process their water..
Mike