I struggled to fully run a 20 gallon fresh water tank for about 3 months. I had to salt my aquarium against Ichthyophthirius which caused many of my plants to die off and then caused high nitrite spikes which I believe stalled my nitrifying bacterial cycle. Anyway, this stuff actually seems to have solved my problem after about 4 days as the nitrites have now dropped to zero over a 24 hour period. I took more than just the starting dose and poured some directly onto my charcoal filter to help it set in.