a&p pellets

I have found many suppliers in my area for a&p and was looking at changing Buzz over to this as ive seen a couple of soft poos over the last few months. he eats plenty of hay and it seems to correlate with when he's in with more food than i normally give him (mum sees an empty bowl and thinks he ahsnt been fed!!). the thing is the easiest way and best value is bigger bags, but how long will one 20kg sack last once opened before it goes off? obviously theres a best before, but thats for when its sealed. and whats the best cheaper pellet for guineas?

My sack normaly has a sell by date of three months, I could never use a hole sack in that time so sptill it with Diddeen

thanks, and what about a good guinea pig pellet, but preferably not as expensive as SS! i looked at a few cheap brand things but they were no better fibre content than a mix!!!