I just finished removing all the gravel from my low tech 75g tank and replacing it with coarse sand. As I was taking the old gravel out, I noticed a lot of black grit that looked liked ground up charcoal. I finally realized that the black stuff was the remains of the Seachem Flourish Tabs that I had been putting into the gravel substrate over the years. Yuck. The sand I’m using now is CaribSea Peace River and I’m wondering if the Flourish Tabs will be the best substrate additive in the long run? I really like the look of the sand and I’m worried about the accumulation of black grit from the Tabs. I use Thrive C as my fertilizer for the water column. Should I switch to Thrive Tabs? Which substrate fertilizer gives the best results over time?