A large container (approximately 3 gallons for a class that will have 6 groups) of water that has "aged" should be available as a water source for set-up of all microcosms. The aged water should be either aerated or left exposed to the air for at least 24 hours to allow O₂ and CO₂ to equilibrate with the atmosphere. This water also will serve as a control for initial dissolved oxygen, carbon dioxide, and pH levels.

It is helpful to set up the microcosms as simultaneously as possible. Testing the "aged water" for initial chemical conditions can be done subsequently to microcosm setup. Follow the instructions that come in the chemical kits to determine initial dissolved oxygen, carbon dioxide, and pH levels.

Microcosm A - Aged water (untreated)
- Fill a jar to overflowing then seal the jar.

Microcosm B - Buffered water
-Fill jar to overflowing and dissolve 100 mg of baking soda in it. Seal the jar.

Microcosm C - Minnows only
-Fill jar to overflowing, put in four minnow in it. Seal the jar.

Microcosm D - Minnows in buffered water
-Fill jar to overflowing, put in four minnow, and dissolve 100 mg of baking soda in it. Seal the jar.

Microcosm E - Elodea sp.only
- Fill a jar to overflowing and place 6 x3 inch sprigs of elodea sp.in it. Seal the jar.

Microcosm F - Elodea sp.in buffered water
-Fill jar to overflowing and dissolve 100 mg of baking soda in it. Place 6 x3 inch sprigs of Elodea sp.in it. Seal the jar.

All microcosms should, ideally, be placed in a sunny window or under grow lights to facilitate photosynthesis by Elodea sp.and serve as an additional control for conditions in all microcosms. Allow approximately 20-30 minutes for conditions to change in the microcosms. It is unlikely that minnows will become distressed during this time.

Sample Collection
Oxygen samples should be collected first from each microcosm. Collect approximately enough water from each microcosm for your DO test, being careful to avoid creating turbulence and splashing. Oxygen levels will change if excessive turbulence is created. Follow the instructions included with the LaMotte or Hach kit for determining the dissolved oxygen level in your sample. Record values.

Remove minnows and plants from the microcosms following collection of oxygen samples to avoid further change water quality changes.

Carbon Dioxide Sampling - Collect samples and test following instructions in your kit. Record data.

pH Sampling - Collect samples and test following instructions in your kit. Record data.