Does the ammonia guard work right away? Is it safe for the fish? Is that the best thing to do at this point?
55 gal? As other have said - the fish are not appropriate for that size tank. As they grow - they will either get sick and die from the stress of an undesized tank - or kill each other from overcrowding in the tank.
The best thing to do is take the fish back to the irresponsible fish stores that said it was OK to add SIX fish to an uncycled tank. If they refuse to take them back - find someone local that can take them off of your hands. You may still choose to buy from these stores - but do your own research as they are OBVIOUSLY NOT GIVING YOU THE RIGHT INFORMATION.
Your only hope for them to survive in your tank will be constant daily water changes to keep the ammonia and nitrate levels down. Even after the tank cycles (which will take a long time as the water changes will slow this) - you will have water quality issues with that many large fish in a 55gal (especially as they grow).
Some LFS give good advice - but most do not take the time to look at all of the variables that can be in out tanks. They may miss some detail (or ignore it)- like the fact that the tank has only been set up for seven days. Even IF the tank is already established enough to not have a cycle (THIS IS
EXTREMELY RARE)- you will not be able to tell in 7 days. You would need to be testing constantly (daily) for at least 2 weeks AFTER adding something that would break down in the system (like a raw shrimp)
If the LFS is telling you that you now need some chemical to help with ammonia ----- well----- why do you think you need to but more chemicals from them? --- they are not always concerned with the long term care as long as they can keep selling you things to limp a setup along.
At the top of the newcomer forum is a sticky link of a lot of great articles. READ THESE - especially the ones that cover the cycle.
Best piece of advice you will get here --
NOTHING GOOD HAPPENS QUICKLY IN A SALTWATER TANK
- so, if things seems to be going toooo fast (like adding six fish at once) well, it probably is.
ALWAYS ASK QUESTIONS- even if you do not like the answers. This site as a ton of great members, many of which have maintained successful tanks for years. If you have a choice between listening to a LFS --- and the advice here, take here 1000%.
To help with answers - is is always useful to post (or add to your sig) your tank specifics. Tank size, water test results (and HOW you tested for them), filtration methods, lights, ect. The more information, the better.