Hi, after some advice!

I have just added 8 6.5cm Stendker discus to my new tank (240l). Tank has been up and running fully cycled with 20 cardinals for the past two months.

2 days after discus added my ammonia jumped up to 0.5ppm. (Previously 0). Nitrite is currently 0 and Nitrates about 5ppm.

Iíve changed about 75% of the water over the past 36 hours and ammonia down to 0.25ppm.

I have reduced feeding (beef heart) and added prime and purigen.

Iíve also added a dose of filter starter.

The fish all seem fine. Any advice on next steps?