I have been using Flourish Iron for a while now and wanted to switch to something less expensive so I decided to order some Chelated Iron 10% DTPA from aquarium fertilizer.com. Well they accidentally sent me Chelated Iron 13% EDTA instead. My question is if this type of Chelated Iron is safe to use and if I were to use a 500ml bottle and dose at 20ml what would be the mixture? Thanks for your help. Much appreciated.