Confused About Adding Fish

The man at the shop has no idea about fishless cycling and is advising how to stock when doing a fish-in cycle. Lots of shop workers are like this, though most will also try to sell you a bottle of bacteria.

With fish-in cycling, the fish have to be added a few at a time, doing a water change whenever ammonia and/or nitrite read above zero. Once they remain at zero the next batch of fish can be added. But the man at the shop probably doesn't believe in testing and water changes either, just add a few fish, wait a few days and add a few more, and if they die come back and buy more.

Has he said he refuses to sell you all the fish at once or just advised against it? If yes, can you find another shop? Or perhaps get a group of friends to go shopping with you and each buy one species of fish (which you'll pay them for outside the shop!)

Fishless cycling means adding ammonia to a tank to grow more bacteria than a tankful of fish needs. If done properly there should be no ammonia spike (or nitrite spike, he forgot to mention that). That's the whole reason for doing a fishless cycle, so that all the bacteria are there in the tank before fish are added.

With fish-in cycling, fish are added to a tank with virtually no bacteria and the waste from the fish feeds the few bacteria in the tap water (bacteria which have managed to escape being killed by the chlorine or chloramine that the water company adds to kill bacteria) till enough have grown to deal with the ammonia/nitrite. With fish-in cycling, there is an ammonia spike, followed by a nitrite spike, which is why the fish keeper has to do a lot of water changes to remove the ammonia/nitrite to stop the fish coming to harm. it can take weeks of daily water changes to do a fish-in cycle without harming the fish.

The man at the shop has no idea about fishless cycling using ammonia to grow all the bacteria; he knows only about fish-in cycling. But you won't convince him otherwise, unfortunately.

Years ago, fish-in cycling was what everyone did. No-one really knew about the nitrogen cycle and bacteria 'eating' ammonia and nitrite. They just knew that if you added too many fish at once, or added a few at a time but too quickly between the batches the fish got sick though no-one knew why. So everyone learned to take it slowly, and even so fish still got sick but some made it OK. They did know that if they added salt to a tank the fish didn't die as often - we now know that the chloride part of salt stops nitrite attaching to the blood during the second stage of fish-in cycling. Some old time fish keepers still say salt should be used routinely.
The nitrogen cycle has been known for 30 years, and fishless cycling was developed from that knowledge, but there are still a lot of people who are stuck in the old ways.


If the man at the fish shop also says not to do water changes, that too is old school so ignore him. We now do weekly water changes not once every few months