**My question: do I purchase 6 or 7 bags of sand, and should I deviate from the 5:1 ratio (see math below, or skip to Option A/B/C)?**

I have a 48" x 18" x 18" tank. My heater is 11" long, so I don't want my substrate to exceed 7". With a 5 sand: 1 eco earth ratio, sand cannot exceed 5.8" or 2.9 cu. ft. Each 20kg bag of play sand is 0.45 cu. ft, therefore, I need 6.4 bags of sand.

If I purchase 6 bags of sand, that totals to 2.7 cu. ft of sand, or 5.4" height of sand (or 6.48" when mixed with eco earth). With 7 bags of sand, that totals 3.15 cu. ft, or 6.3" of sand (or 7.56" when mixed with coco fibers).

Option A: buy 6 bags of sand, and mix enough eco earth to reach substrate depth of 6.48"

Option B: buy 6 bags of sand, and mix enough eco earth to reach substrate depth of 7" (not sure if more eco earth is okay, or if it'll be too much moisture in substrate)

Option C: buy 7 bags of sand, and mix enough eco earth to reach substrate depth of 7.56", knowing that 0.56" will be above the bottom of the heater.