I have a 20g tall tank for quarantine, acording to bottle im adding 5ml for every 4 gallons of water, so i added 25ml of copersafe (liquid). with hanna checker it reads 1.92 i added 5 more ml of liquid and it still reads 1.92 added 5 more ml. and tested next day. im at 1.92 Im afraid to overdose, hanna regants of coppersafe by frits is not to expire untill next year.