How many calories? Fasting is about caloric intake and insulin response, not Atkins-style “net carbs.” If calories are less than 50, it might not affect weight loss, but it will still be considered a “dirty fast.”
Psyllium husk fiber is soluble fiber and you do get a few (2-3) calories of energy from each gram rather than the typical 5 calories per gram of carbs.
You should keep in mind that 20g in a day is beyond the recommended 3 servings.
If you are trying to spread that out, it seems a reasonable solution would be 10g to break fast before dinner, and 5g before bed or first thing in the morning.
If anything, soluble fiber regulates blood sugar, and the plain psyllium you’re eating doesn’t have any sweeteners. The calories (20-30) are insignificant for weight loss and would be beneficial if they help you not eat beyond your calorie deficit.