Definitely go to hardware store for sand. It’s like 3$ for 50 lbs (I use two for a 50 gallon). Coco is best to get off of Amazon in the brick size. 1 brick will expand to ~3 gallons (I use two for a 50 gallon). With a 75, you’ll probably need 3 bags of sand and 3 bricks. https://www.amazon.com/dp/B08XX68QJM/ref=cm_sw_r_cp_api_i_EYAF1SRQEXD4W7D92FCV Shouldn’t gouge you too bad.