I supppose it's personal preference for me. I increase TA with Baking Soda and increase pH with Borax; seems to me it's more targeted - just my thinking, either way will work. BTW, it will take twice as much (by weight) Borax as Washing Soda to have the same effect on pH.
Swamp Mistress ( http://www.poolforum.com/pf2/showthr...-it-all!/page6 ) seems to have had luck with a series of improvised filters.