Hi Sean
I like to help you troubleshoot your system to see what could be the possible cause of your PH swings ,however first I like to clairfy a few things
1-Ocean pure Pro is designed for more demanding tanks & is fortified with all the elements so you don't have to dose anything to balance the salt mix
2- I did contact manufaturer this morning after reading your post ,there has been no reports of a bad batch ,I even provided him with the batch number of the products that we have distributed in the west coast in the past 3 months & no reports.
keep in mind each salt batch is in kilo tons ,therefore if there be any problems it will be all overplace ,CANADA ,US ,EUROPE & ASIA.
3- Your MG reading is abit high however even @ that point you will not have any IONIC Balance distruption of any sort AS YOU MIGHT THINK.
4- This is the same salt I am using on my own system & many other people here & calgary with no repoted problems.
Now back to the possible cause of your PH SWING
1- As far as the chemistry
I think Albert hit the spot ,what I am getting from your post your are complaining that the extra MG is not allowing the formation of the CACO3 crystaline solid,well you do not want the recalicification happen in your water column any way ,i could not understand the point there?
2-Also you do not have any free radicals in your water so when they say the concentration of a certain element that means the available Ions of that element that are balanced in the mix ,if you mix your salt with water you do not have CA+2 IONS free in the water ,it is in your solution balanced with the positive Ions of the same but opposite charge.
so I can not understand the relation you are trying to make between the readily available CA & CACO3.
3- I have thought hard how 300 ppm more of MG in the mix can be the cause of PH swingsbut didn't come up with anything
now please let us know about the following
1-what brand test kit are you using @ what resolution?
2- what is the salinity of your mix?
3-are you using any ca reactors ,what is your co2 injection rate? is it on a timer or controller?
4-what is your Kalk dosing schedule & how much & what time how do you mix your Kalk?
5-how often you water changed with the mix you are refering to & what is the xolume?
6-what is your tank size & your total net water volume ?
I am sure other people can chime in as well
However I know Albert is very knowledgable & he can also help you if you paid him a visit ,since he said you are a good guy & a good customer ,I think that be a good Idea as well
Speak to you soon
Regards
Proline