I see you had posts for stocking advice just almost exactly one month ago. You also mentioned no water changes. How fast did you add all stock? Typically you want to slowly build up your bio load because your bio filter lags as it needs to populate to eat the new waste, especially in a smaller 30g total system tank. Although it definitely quite possibly be velvet, I wouldn’t count an ammonia spike out of the question.
You’d want to go a single fish for 2 weeks, then add another, the. Possible add twice the mass, etc. with no water changes, no skimmer, very little surface area quickly looking at your scape, you might not have the bio filter capacity as many wasteful stock was added almost simultaneously.
This hobby is all about testing your patience as doing the opposite often leads to disasters.