I'm assuming you meant 1 gram of that thing contains only 6.25% of SN (will make it 6% to make it easier).
So, you need 20 g of pure nitrite (well, at least 95% pure so so so) to ctb successfully.
1g X -- 6 % SN
xg X -- 95% SN
95/6= 15,8
Answer: You'll need at least 15 g of that thing to make 1% of the recommended SN concentration %.
To ctb with that you'll need 1425g of that to make up for 20g of 95% or more SN. So, 1 kilogram and almost a half lmao.
15 g -- 1 %
X g - 95 %
I'm just trying to show you how absurd it is to try to replace it with that thing you have with low concentration, even if my calculations are wrong, you'll need a bunch of that, and you won't be able to swallow it all, you'll die choking, not by the SN effects.
Ofc you could purify it by doing some chemistry, but that would be more expensive than to just buy the normal SN with high concentration.