What’s caused the am­mo­nia cri­sis that’s killing our cat­fish?

Practical Fishkeeping (UK) - - Fishkeeping Answers -

We have a 105l/23 gal tank which is run­ning just great. We also have a small 28l/6 gal tank which is mainly for poorly fish, but re­cently our Bristlenose cat­fish bred so I moved 60 ba­bies into it. The next day I found 10 dead and a fur­ther eight dead the day af­ter that.

Our prob­lem is am­mo­nia – it was 6, but is now run­ning at 3. We have put an Aqua-detox in the fil­ter and I also put 20g of tonic salt in to see if that would help get rid of the am­mo­nia.

All the other pa­ram­e­ters are low, but they have been since the tank was set up around three months ago. How can I solve this prob­lem? CHRIS KERRY, BY EMAIL

BOB says: It sounds as if your small tank is not ‘cy­cled’, the process whereby you al­low the fil­ter to be­come colonised with the vi­tal ben­e­fi­cial bac­te­ria which con­vert toxic am­mo­nia pro­duced by the fish to the rel­a­tively harm­less ni­trate. Keep­ing a small tank for emer­gen­cies in the man­ner you do is a good idea, but the fil­ter will not be ma­ture un­less you reg­u­larly add small quan­ti­ties of am­mo­nia to the tank when it’s empty of fish to keep the bac­te­ria fed. Sud­denly adding a large pop­u­la­tion of fish means that the fil­ter just can’t cope and the dan­ger­ously el­e­vated am­mo­nia lev­els and fish deaths you are ex­pe­ri­enc­ing are the in­evitable re­sult. Adding the Aqua-detox will help to re­move some of the am­mo­nia, but will not solve the prob­lem of the im­ma­ture fil­ter. My ad­vice would be to carry out im­me­di­ate daily 50% wa­ter changes with dechlo­ri­nated wa­ter to keep on top of the am­mo­nia prob­lem, while the fil­ter starts to catch up.

Bristlenose cat­fish need well aer­ated wa­ter with a cur­rent to thrive.

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