i have recently setup my mbuna cichlid tank using mature filter sponge, everytime ive tested ammonia has been 0 but nitrite has been really high. even when i do water changes it dosnt bring the nitrite down
Test your tap water for nitrite, if you are diluting your tankwater with water containing less nitite it is not possible for the tank concentration to stay the same
When i kick started a filter with mature media for my gourami tank,it went into a mini cycle with the nitrite,after a week or so and daily w/c's it finally disappeared.