I use at a rate of .125grams per gallon as a foliar feed or soil drench but I also add fulvic for foliar and humic for soil drench at a rate of .35grams per gallon
This is what Greenleaf says it can be used at wide range of rates:
Previously we were using the traditional type extract (black color) which was pretty good, this new version we have its made with an advanced low temperature extraction method, and doesn't filter out any chlorophyll at all from the seaweed so it retains a golden/yellow color. As far as the auxins/cytokins/IAA and alginic acids, this is the highest available purity currently now. So if anything you could even use less dosage compared to standard black kelp extracts. You can use in a pretty wide range honestly, from 0.2g per Gallon, to even 5g+ per Gallon. For foliar would recommend maybe 1-2g/Gallon, and root drench maybe 2g/Gallon as a safe range, but you can also do far less if you want.