Quote Originally Posted by vafa
It's a tetra small bio bag
This? Is there anything else in the filter?

Do you have just the carbon in it? If so you would be far better served with actual bio-media in it instead of carbon. I suspect this is a major reason for your issues.

If it were me, I would dump the carbon out and replace it with this or similar. It would hold far more BB than the carbon is capable of [Not it's role really, Carbon is chemical filtration and you need biological filtration] and it also doesn't lose it's effectiveness like carbon does. I don't run carbon at all.