Aquarium Math: Tank Volumes, Water Changes, Dosing & Stocking

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Calculate the gross volume of a rectangular, a cylindrical and a bow-front tank, convert litres to US gallons and find how much water the rectangular tank really holds once substrate, decor and the gap below the rim are taken off.
• Calculate what one water change does to a reading, find the level the tank settles at with weekly changes and steady build-up, project every week with one closed formula and work out with logarithms how many weeks it takes to get below a limit.
• Compare four water-change schedules by the low and peak reading they settle at, flag the ones that break a fictional limit, compare the water they use per week and calculate the smallest weekly change that keeps the peak at the limit.
• Turn two fictional product labels into millilitres: water conditioner for the new water of one change, rounded up to the cap marks, and a fertiliser stock solution to reach a target level and to top it up after each change.
• Size a heater from the water volume and the temperature difference with a fictional rule, pick the smallest stocked size that covers it with a lookup, and check whether a filter's real flow reaches a fictional turnover target.
• Turn a fictional stocking rule into numbers: the load of each group from adult length, count and body shape, the tank's capacity, the current load as a share of it and how many more fish of a candidate group would still fit.
• Turn the watts and hours of the tank's devices into kWh per month and a monthly electricity cost, then price an LED upgrade by its yearly saving and payback time.
• Smooth twelve weekly nitrate readings with a 3-week rolling average, count the weeks outside a fictional target range with COUNTIF and COUNTIFS and show the readings as a line chart.