I have not heard of using Vitamin C powder as a dechlorinator so can't comment on safety/dosage.
Most shop-bought dechlorinators use Sodium Thiosulphate so the best thing is to use one of those. If you're cost-conscious, try Seachem Safe, a powdered form of Prime which is used in tiny quantities and very economical to use.
Hi, thank you for the response. It is precisely why I am seeking alternate methods, the declorinators are expensive when you have multiple tanks. RO system is my next step when I add more tanks, but for now I cannot justify the cost - and RO has its own attending costs too.