The 150g tank is my oldest tank. It has gone through periods of looking pretty good and other times where it was not so good. It was time for a change and I had recently discovered a source of the sand blasting substrate Black Beauty which is really nice looking and dirt cheap. I have used it in some smaller tanks with success so decided it was time to try it in bigger tanks. Over the last weekend, I scooped out all the old substrate and replaced it with 200lbs of #3 (medium) Black Beauty for about $30.
The 72g tank has always been an afterthought. It was going to be wht the 240g became, but partway through the build I determined it was too small to do what I wanted. I was then going to make it a cichlid tank but it's kind of small for African ciclids and I never really got it to a point I liked for South American cichlids. So with inspiration from some Amano articles in recent issues of Tropical Fish Keeping magazine, I replaced the gravel with 100lbs of Black Beauty #4 (fine) for $15 and redid the hardscape.
For both of these tanks, I treated all the wood and rocks with hydrogen peroxide or bleach to kill off a growing infestation of black beard algae (bba). Hopefully with good fertilization and high CO2 I can keep it at bay. For my other tanks, I'm trying to get rid of it without wholesale change in the tank. The 60g I'm just using high CO2 and the 240g I treated with Flourish Excel and following with high CO2.