Yep... thats the decision I came to as argos is only 0.3 miles from me and the beach is about 30....
I got 2 bags to be on the safe side for my 3ft tank but they ALWAYS have it in stock so you can top it up any time....
I used the argos paysand in two of my tanks and also in a couple of my reptile tanks, and Ive nothin bad to say bout it.
will a good wash its idea for fish tanks