saltwater aquarium setup help

I purchased a used 24 gal bio cube. The tank was extremely clean and well taken care of. I set the tank up with live sand and several live rock along with several peices of brand new rock. I also purchased the stuff (cant remember the name of it) from Petco that adds bacteria and makes the tank ready for fish immediately. I tested the water to make sure all parimeters were correct. The tank set for 24 hours and then I added 3 damsels which died immediately. I teted the water again and it was perfect. The previous owner assured me that the tank was only cleaned with water and vinegar and there was no odor of any chemicals inside the tank. Any suggestions in what could be the problem or what I need to do with the tank? Any suggestions would be greatly appreciated!

IMO those chemicals do not work and its really a waste of money.Salt water tanks takes alot longer then 24 hrs to cycle!Our SW experts can help you better than I can!Welcome to the box!

Be patient, I waited almost a month to add fish and corals to my tank. Even when using live Rock from the beginning the tank can still take a while to cycle.

There are a whole lot of things that could be wrong here. What do your tests say about the water?

Edit to add... Are you using saltwater tests?

there is no Bacteria in a bottle that will cycle a new tank in 24 hours, although I do use Stability and Bio Sprira with great success and have been for the last 3+ years I always use seed water and dirty Chaeto along with it to start my tanks and even then I wait to add fish. your params are probably reading 0 across the board because the tank hasn't even begun to cycle. if you know someone with an established tank ask them if you can have their w/c water and Chaeto or you can buy some Chaeto from your LFS to help seed your tank. a good sign your tank is beginning to marinate are Diatoms they look like brown dust all over your rock and sand bed you'll know when you have them. good luck and slow down nothing good in a saltwater/Reef tank ever happens fast.

P.S where in Va are you? I will give you all the seed water and Chaeto you need.
wait a minute, I just noticed it says under your name you already have a saltwater tank?
why don't you seed it with that one??? I'm a little confused here if you already have a saltwater tank then you should already know all this

I made the same mistake by setting up my tank with LR and LS, adding the bacteria-in-a-bottle and thinking everything was okay to add fish. I put in 2 damsels and 2 cardinals and a few days later 2 peppermint shrimp. Within 2 weeks, my tank was in full cycle, the nitrates were off the chart in spite of daily water changes and maintenance and cleaning the filter pads of my E 400 daily. I lost a cardinal and a peppermint shrimp within a day or so of each other. That's about the time the diatoms took off.

I learned the hard way that no matter how excited I am to get my tank inhabitants, I should never rush the process. I didn't have access to any seeded water, so was just using regular water with the water conditioner in it.

I'm assuming you used a dechlorinator/water conditioner if you used tap water....otherwise all your bacteria in the LS and LR (as well as the stuff in the bottle) would most likely have died off. Also, did you clean out the tank before you set it up? Even if it looked clean, there could have been some sort of residue (pesticide, exhaust, etc) sticking to it that had settled on the tank especially if it had been stored somewhere like a garage... Just a thought.