Bristlenose don't tolerate salt as well as common plecos so I would go with no more than 1 tsp/1 gal, maybe less, keep an eye on its eyes and nose bristles, if the bristles start to turn pale on the ends, or the eyes start to cloud do an immediate 50% water change without adding more salt. I have not kept many of them and the ones I had stayed healthy so the only salt I used with them was 1 tbsp/5 gal.