This week we learned that BTB can be used to check for acid in water. So, we gathered 4 water samples and tested them. First, I grabbed a sample from a faucet in the school building. The others came from our portable classroom. We took two samples from the water cooler. One from the water cooler itself and the other from the overflow tray. Also, we thought it would be interesting to see if there was acid in our fish tanks we’ve set up around the class. In each sample we found acid, except for the tap water. How did the acid get in the water? The class came up with lots of variables that could have been the cause. These are factors that can change and affect the outcome of an experiment.

fish
fish breathing
temperature
gas
fish waste
food waste
bacteria

The kids decided to run an experiment and to try and change the variable called fish. We placed 3 cups out and filled them with 100 ml of tap water. We knew tap water didn’t have acid in it; so we’ll use it to see what might be linked to the cause of the acid. Next, we put a fish called a guppy in one cup and a plant called elodea in another cup. The 3rd cup just had water. Last we put 6 drops of BTB in each cup to see if it would change its color from blue to yellow, which indicates acid. Nothing happened at first. We decided to wait 30 minutes. Below is a picture of the experimental set-up.

Do you remember what happened? The cup with the fish changed color. The elodea stayed the same and the cup with nothing stayed the same. So, how did the fish cause the water to change? The video link below reveals what happens.