Google translation:
Hi there
My name is Christophe and I am French.
I raise HECKEL CROSS discus in a 240 liter bare tank with an external JBL 1502 filter and three Hexauster filters.
I change 50% of water every day and despite that I still have nitrites, luckily I added three doses of SAECHEM PRIME.
What am I doing wrong?