Planted Tank Guru
Join Date: Nov 2009
Location: Missouri united states
A sprinkling of Osmocote (little goes a long way), under a cap of Flourite,Safe-t Sorb,or plain unscented cat litter (no additives) could work well.
When I last set my 80 gal low tech planted tank a couple year's ago, I used 1/2 cup of Osmocote as sprinkling on the glass before covering it with dirt,and then a layer of safe-t-sorb to cap it off.
This is decidedly not something for those who uproot plant's a lot .