The maintenance math, grouped by the kind of tank you run. The compatibility engine in the builder handles stocking; these answer the day-to-day questions.
Compute capacity from length, width, and height in inches.
Realistic accounts for ~12% displacement from substrate, rocks, and equipment. Use this when planning stocking.
Size the heater from tank volume and how far it must lift above room temperature.
Snapped up to the nearest standard retail size. Always run a separate thermometer; heater thermostats drift.
How much water to change to dilute nitrate from a current reading to a target, as one change or a gentler series.
A change over 50% can swing temperature and chemistry hard enough to stress fish. Prefer the series unless it's an emergency.
Convert between specific gravity and parts per thousand at 25°C / 77°F.
Linear approximation valid in the hobbyist range. Temperature affects density. Refractometer readings drift by ~0.001 SG per 3°C of temperature swing.
How much marine salt to dissolve to bring a volume of RO/DI water to a target specific gravity.
Approximation: grams ≈ liters × ppt, with ppt ≈ (SG − 1) × 1300 at 25°C. Brands vary a few percent. Mix into RO/DI, circulate until clear, and verify with a refractometer before use.
Grams of sodium bicarbonate to raise alkalinity from current to target dKH, with a safe daily limit.
Dissolve fully in RO/DI water and drip into a high-flow area. Re-test before each subsequent dose; teaspoon mass varies with packing, so trust the test kit over the spoon.