.3 is a lot, especially if you have aragonite in the tank should be soaking most of it up. It is going to unbind for the rocks and sand for a while, so leave it in there until it turns blue no more. You can regenerate it with a high concentration of HCL and it is as good as new - be careful with the HCL which is quite safe for smart people, but can be quite dangerous with morons.
I use IO. It comes in the 4x50lb bags and I ordered a pallet last time cheaper than the last few group buys for Kent. It is a high quality salt that is cheap. If you know nothing else about it, RHF uses it...so that might be good enough for some people. I have been using it since the early 1990s with no issues - I have tried others here and there but always come back to it. I used to mix IO and Oceanic 50/50, but the redesign of IO in about 2009/2010 took care of all of my issues. A 50 gallon bag mixes up in a 44G brute container just perfectly and with about 1ml of HCL it makes my alk about perfect for the SPS tank - I don't do anything with the mixed reef. IO is really bad about settling (like most salts are), so you REALLY have to mix it dry if you are not using the whole container or else the params can get out of whack... actually, everybody should be dry mixing their salt.
