Seachem makes superior supplements to kent. There I said it. The seachem line is great and I love it. The products have been used and tested for about a decade. Their salt however is less than a year old. I believe that in time, they will refine their salt mix, but currently i am not impressed. I have used a total of 4 x 160 gallon buckets and had consistently low alk, as well as sediment at the bottom of my mixing drum.
Additionally, on one bucket, I experienced precipitation on the walls of the container. Once it has used in the tank, all was great, polyp extension etc. Some minor diatoms occured after a 33% water change.