So I want to start out by saying I have never had a sand- sifting goby. However, I have used blasting sand in several tanks with the same results, both freshwater and saltwater. Both did just fine, and I never had any issues in my reef tank with blasting sand. Now, I will admit that I am not an expert, however, I know a little bit more about blasting sand, given my experience not just in the aquarium, but also using it for work for about 7 months. A lot of people are still under the impression that blasting sand is sharp, but that's not true anymore. In the old days, you might have a sharpness. Nowadays, there isn't much of a difference between normal sand and blasting sand when it comes to sharpness. The only thing you have to look out for is the fine or coarseness of the sand. Bottom line--20/40 would be a good, cheap substrate for your tank and I do not think the sand was the cause of your goby's death.
