drinking safe hose into the tank is all I do, straight from the washing machine feed. I add 6 1/4 teaspoons of seachem safe as it fills. I do about 175G changes once a week for about 275G of water.
but someplace like this might have what you want.
Are you sure about that dosing? That amount seems awfully high.
Get Seachem Safe instead of Prime. Safe is a lot more concentrated than Prime and will last you much longer.
This, Safe is just a powdered version of prime and if you buy the large container of it, it's essentially a lifetime supply since it will treat about 800,000 gallons