I get my dry ferts from Greenleaf Aquariums.
a lot more fert for your $ - depending on tank(s) size, the fert package from GLA could last up to a year for the cost of 2 liquid bottles that may last a couple months
you have to measure each dose with a gram scale depending on tank size and ppm desired. There is a sticky in the Water Params giving general instructions on how much to dose. I made a chart and kept track of my measurements and ppm readings and adjusted accordingly.