For those who don't know Matrix is nothing more than white pumice stone that has been "acid washed" which is rather a dubious thing given it has never been proven scientifically that that process is of any real benefit other than the benefit of color uniformity and the profit swelling it provides Seachem's bottom line.
Also given this is simply stone any of their precious dosing specs are rather immaterial.
More is better because why not.
Also again why pay what 3x more for the same thing?
Yes another forum actually paid a lab to determine what Matrix was and tada! Pumice.
So save your damn money. Or pay for their pretty bucket and label. And the fact that they washed and effectively bleached it. Yeah I'll take the 15 pound sack please lol http://www.generalpumiceproducts.com/order-here/
If you want "matrix", you not totally sure if pumice stone is the same thing (I think it is, but..), and you don't want to pay exorbitant prices .......
Seachem matrix is expensive. Then there's a "pond matrix" which is cheaper, and made by Seachem even. Then there's "pumice stone", which nobody in my hometown has locally. So, I just bought Pond Matrix.
If I had it do over, I'd just buy "pond matrix". Ya pay more, but you're buying it once and it'll last decades. to know I have the right stuff in my filter, I figure I"ll take the drubbing once in a lifetime.