As has already been explained to you the once weekly hit with 7x dichlor takes care of the chloramines. The reasons MPS might be used instead are situation dependent. For example, your total chlorine reading is already high (say 5 ppm or more) and you need to shock. At the same time, you want to use the tub on the same day you shock. MPS would be a better choice in this circumstance.
The use of MPS will increase total dissolved solids more than the use of dichlor for shock. While I think it is fine to use MPS for shock as per above, dichlor is preferable for most situations.
As has been suggested already go to Doc's website (rhtubs.com) and check out the Vermonter's detailed information on dichlor. I am totally convinced that his approach is superior to any other I am aware of.
Regards,
Bill
Regards,
Bill