Sorry but there's too much wrong with this advice. First, if you add a bacterial supplement you need to add the fish right away. If you wait and leave the bacteria without an ammonia source they're probably going to die. Second the fish weren't gold gouramis. In the course of this thread they were positively identified as a variant of WCMM. So, not nearly so bad! Third, substrate is not essential. The vast majority of the bacteria grow in the filter where there's higher oxygen and nutrient flow. There will be a few sticking to other surfaces but not a significant number.