The official SI unit for volume is the cubic meter, but for a fish tank, I would use liters. One liter is one cubic decimeter (or 1/1000 of a cubic meter).
liters
kilometre
a centimeter
you would use grams
I am guessing you can use Gallons.
gallons
If you measure properly, the amount of water does not change. Measurement with whatever graduated cylinder you choose will not alter the amount of liquid measured. Most people choose to measure once with a larger one, but if the amount of liquid falls between the measurement lines, you can measure the "leftover" with a smaller cylinder and find the exact answer.
It depends on the amount. Very little: mm3 Drinking Glass: cm3 Pools: m3 Oceans: km3
I wiil use water
The unit of measurement for milk is litre (L) in the SI.
To measure weight you would use Kg To measure height length or girth you would use metres
It depends on what characteristic you want to measure! Its mass, its height, the amount of body fat, the fineness of its fleece?
gallons
You can not measure the volume of a liquid with a measurement designed to determine length. A centiliter is a measurement of volume, or the amount of space that a liquid can consume inside an object. A centimeter, would be a measurement of length and a centigram is a measurement of mass (weight).
a time watch in seconds
typically, acresMy VersionI measure a lake in surface area, Square Miles in my case, and Ice thickness for safety. As you can see my measurement is for my uses.You may measure the amount of water, the depth of the water, The cleanliness of the water, the height of the lake above sea level or dozens of other ways depending on what you need to know.
Hours and minutes would be a sensible measure of the amount of time you spend on homework each day.