You have a good question. Shouldn't the chemicals have the same ratio of use whether treating or recharging. I think they do, but see the discussion below and let me know if you agree or you see an error in my math or logic.
First, (ignoring that one is dry and the other a liquid), Safe and Prime are not identical. Prime includes additives that handle metals and that are chemical stabilizers. That's why Safe has to be used soon after it's mixed. They are highly similar and for most people can be thought of "similar enough" to be interchangeable. In almost every case it doesn't cause a problem to call them the same. But they aren't truly the same.
It's possible that Seachem thinks there should be a different concentration (relatively speaking) between treatment and recharging due to how Purigen adsorbs. I can't say but it's worth considering.
Treatment:
Prime 30 ml for 300 gallons
Safe 1.25 tsp (6.25 ml) for 300 gallons
Ratio: 30:6.25 or 4.8. You need 4.8x as much prime as safe to treat.
Recharging
Prime 56 ml for 1 cup
Safe 1 tbl (14.9 ml) for 1 cup
Ratio: 56:14.9 or 3.8. You need 3.8x as much prime as safe to recharge.
Comparison is 4.8 to 3.8.
Keep in mind that treatment instructions are often "rounded" for simplification or ease of use. One cap full happens to be a better instruction than .8 cap fulls. 1.25 tsp is better than saying 1.14 tsp. So the ratios should not be expected to be exactly the same when comparing treatment to recharging. I'd bet that if Seachem provided the exact amounts that the ratios would be identical, but that simplifications in the instructions are causing it to be off.
But 4.8 to 3.8 indicates it's probably meant to be the same ratio whether treating or recharging.
