Moisture In Sodium Chlorite Powder

I ordered a pound of Sodium Chlorite Powder so that I can make it for family and friends.. Plus I feel the need to stuck up on it. When I received it.. It had obvious signs of moisture mixing with it... Instead of it being a powder it was a HUGE SQUARE BLOCK. In order to make MMS I have to chip pieces from the block then grind it into a powder.... When I make MMS it seems as if it isnt as affective.. (I've made MMS from Sodium Chlorite Powder before but from a different supplier). When I mix it with citric acid it doesnt become a dark brown yellow color.. It' a light yellow collor and it take about 5 minutes to get to that point.... I know its not citric acid cause its pretty simple to mix (although that was in block form also)........So I'm wondering... If the moisture causing problems or what.........And if so can anyone suggest where I can purchase Sodium Chlorite Powder thats shipped and REMAINS in powder form......