Some brands have a little more phosphate than others, none have a lot of phosphate. Some have more magnesium than others. I would mainly make my determination based on price. Magnesium is easy to add with a reactor, just put a little dolomite in yur reactor occasionally, it is available at plant nurseries or green houses in small quantities as gravel, a little bag is all you will ever need. If you use Kalkwasser as ATO water then phosphate will not be a problem as the Kalkwasser will precipitate out your phosphates. A combination of a Reactor and Kalkwasser is better than using just one of them. One tends to cause a low pH and the other tends to cause a high Alkalinity, so they balance each other out real well. Plus one adds phosphate and the other precipitates phosphate. They make for a good partnership. Better than most marriages.