Join Date: Feb 2018
Location: Puget Sound, WA
I think it all depends upon what plant you want to grow. If its lower light, low tech like anubias, ferns etc then do a few good gravel vac jobs and be done with it. If its stem plants then I highly suggest ditching the entire substrate for new.
About 2.5 to 3 inches max height is good.
A brand new bag of Eco Complete would fill that tank haha. Try out Fluval Stratum or something similar.