Tanks need time to mature, often systems can take 6+ months of running empty before they're even capable of supporting life. Sorry about your clowns, but things like this happen (God knows this is how my first tank went) though it's important to realize that setbacks are part of the learning experience. Here's my advice for you. Let the tank run empty for a few months, don't add anything living and monitor parameters (DO NOT use API test kits, they're often unreliable for parameters like ammonia, nitrates ect, use red sea, salifert or Hannah instead) take it slow, add things gradually over the course of a few months, start off with things like soft corals, snails, hermit crabs ect. The tank is too small for clownfish, though things like barnicle blennies, watchman gobies/pistol shrimp pairs would be perfect. Don't overfeed, check parameters weekly. Don't use swing arm hydrometers for salinity, use a refractometer. Use RODI water (NOT tap water) for the tank, talk with local reefkeepers and ask questions on the forum to build your knowelage. Also i recommend to not shop/ask advice at chain stores like petco, petsmart ect (while some of them may have knowelageable employees and a good fish section many of them unfortunately dont) instead find a good local fish store and ask there. When I first got into this hobby, I jumped in too quickly and didn't know enough for success, and things definitely happened that were avoidable if I spent more time knowing more beforehand. Just take it slow, there's no rush. Also get a wavemaker for the tank, you really need some flow in there.
Good luck!
