Luis,
I wanted to clarify on the different types of goby you both are speaking of. As they function in the tank very differently. I have owned both and have seen first hand the difference.
Unfortunately, both vendors and hobbyists categorize these guys wrong all the time. So if you focus just on the Genre name vs. the Common name when purchasing you should be ok. But confirm also by their coloring. There are other Genres that fall under the category of true sifter vs not really sifter; but I am giving you the two most popular that are easy to get from you LFS.
The Genre - Cryptocentus cinctus. - who can pair with a pistol shrimp and share a burrow. He sifts sand around the burrow; but does NOT spend his days going through entire tank and cleaning sandbed. If there isn’t a shrimp for him to form a symbiotic relationship with, he will still stay relatively close to his burrow. Also, he does not swim up the water column and spray all your corals with sand. I had this type in my 26gal nano with a pistol shrimp- so cute to watch, but I did not consider them part of the CUC.
The Genre - Valenciennea puellaris these are true Sand Sifters - they spend their day going through entire sandbed and making it crystal clean; they do not pair up with shrimp. Mine is the “Diamond” variety who has actual blue diamonds on upper body - so quite sparkly. Since I have a 75 gal, they have a lot of real estate to clean and they really need that. The downside is that they will make multiple burrows and will re-fluff them a lot. Some get more settled, but here is the problem- they swim up the water column and spray any coral in the way with sand. So if you don’t keep up with observing and turkey basting the sand off those corals, they will eventually suffocate.
Luis, I made a conscious decision to have this type of goby in my 75gal - I wanted clean sand and was willing to put in the time to “assist” my goby in where the sand Should be! I wouldn’t have a non-nano tank without one. I just chose Not to put corals on sandbed. However, for my nano I will have a zoa garden, some favia, and a meaty coral all on sandbed so I will Not put this genre in there. In fact, I will not be putting any goby in there as it’s only a 20 gal and I can easily clean myself.
Here is a thread from our friend,
@i cant think That explains in more detail- he cited more genres as well.
Thread 'True vs False… what’s the difference?'
https://www.reef2reef.com/threads/true-vs-false…-what’s-the-difference.925479/