Cycling a tank with fish taken out

[Yoemen]

I had some fish in a tank for about 4 days, then read a whole lot of junk I did wrong, and have now sold them to someone who has an adequate tank for them already setup. My question is this, since the fish had been in the tank for 4 days, to cycle it do I need to start handling it like a fishless cycle, or is there probably enough gunk in it now that it can sustain itself for a while??

[OrionGirl]

I'd start feeding the tank. Yes, there will be some ammonia in there, but you have not way of knowing how much until you test, and of course, the bacteria colonies that are starting will soon eat through the current ammonia and then starve. You could keep feeding the tank about the same as you were feeding the fish, minus a bit. That would keep the bacteria fed while you get a test kit and such. Just don't over do it--you don't want to feed algae!

[mishi8]

You'll need to handle it like a fishless cycle. With the fish removed, any bacteria that has started to grow will die off due to lack of food (ammonia).

[Yoemen]

so fish food will suffice or do I need to start adding ammonia after I test it?

[mishi8]

Fish food will keep the bacteria alive/growing for now, but dosing with ammonia would be more accurate. A test kit will be needed to see that you're adequately dosing ammonia, and to monitor the cycling process.

[Yoemen]

Talked to my LFS and he suggested using AmQuel, letting it sit over the weekend and start putting fish into it next week. His reasoning was that nitrate/nitrite levels aren't nearly as important in freshwater as they are in salt water, and the main thing I want to do is keep the ammonia under control?? He doesn't do fishless cycling though.

[mishi8]

You need to decide whether you want to cycle with or without fish. Nitrite is harmful to fish. If you choose to add Amquel and then add fish, then you'll be doing a fishy cycle, and will need to monitor levels of ammonia & nitrite and do water changes to keep the levels low until cycling is complete.

Since you've already removed fish from your tank, why not go with a fishless cycle? No water changes necessary. If you're concerned with how long it will take, you can seed the tank to speed up cycling, or try adding BioSpira.

If you need more indepth info on fishless cycling, check out this article:
http://www.aquamaniacs.net/forum/cms_view_article.php?aid=31