It has to be cycled before its safe for new fish, it's a bit more than just running it empty. The process takes anything from 2-6 weeks before it can support the mess fish make.
See here:
http://www.theaquariumwiki.com/The_Nitro ... http://www.fishforums.net/index.php?show ... http://forum.practicalfishkeeping.co.uk/...
How many fish were you planning on putting in?
If I were you, I would put a few pinches of flake food in the tank every day for one week. You should also at this time add something called StressZyme, which is a commercial product with live bacteria that helps to cycle plants. You don 't have to add it, but it speeds up cycling.
After a week, it is safe to add in one or two small, hardy fish such as guppies. Don't try adding in any sensitive, fancy, or expensive fish at this time because you are just going to waste your money because they will die. You can gradually add in more fish, just 1-2 at a time about once a week. Don't overstock your tank. A rule that some people go by is for every inch of fish you have (lengthwise from head to tail ) you need to have one gallon of water. Just make sure you know how long the fish you get are GOING to be, not what size they are now ... because they will grow bigger and exceed the size of the tank. And those apple and mystery snails can get pretty big, so allow them to have 2 gallons of water.
pets question and answers,www.5d2d.com One more tip: When you add in your fish, gradually acclimate them to the water by adding just a small amount of tankwater to their bag at a time, doing this over several hours. It will make them less shocked when you put them in the tank.
i take it you already have a fish tank and are upgrading to a larger one.
if i'm right i would move some decorations from your existing tank to transfer some healthy bacteria to the new to build up you filter media. keep checking the water levels (ph etc) to get them as close to your existing tank to minimize stress on the move.
alternatively you could buy a few cheap small fish and run a fish in cycle in the new tank, although i don't like this method myself.
Ant
If you are upgrading then you can actually move your fish after 24 hours. Just make sure to take the old filter and old gravel and move them to the new tank, this provides an instant cycle. Leave them there for about a month then you can remove them and the good bacteria will have established themselves in the new filter.
pets question and answers,www.5d2d.com If its not an upgrade then follow general fishless cycle guidelines.
http://www.cichlid-forum .com/articles/fi ...
You only have to wait about two days. You just need to set everything up and make sure that it works. I asked petco, petzoo, walmart and they all said the same thing. I know not big names, but I have only lost two fish since I did it and it was because they were a sickly batch from the store.: 3
