I had a similar dilemma a few days ago, I decided to drain the tank trash the lot and do it again. Although my reason was for a re-scape.
Not something I fancy doing again but it was sure worth it, personally in a tank that small I would re do the lot.
Dirt tank - 120g 120cm x 60cm x 76cm ( under construction )
Shrimp tank - 10g 60cm x 30cm x 35cm ( under construction )
The Fraternity of Dirt #93