I think McShnutz has a real good point there.
I stopped using fabric pots, but when I did use them there was more often salt buildup on them than not. Nothing enough to bother the plants more than a timely dose of enzyme finishing product bottle will fix (I use BAC Final Solution, works wonders when applied at the right time, to the noticing eye and for the plant, is easy to apply and is great for pre-grow, 5th week flower and 1 week before harvest soil treatment).