Algae grow in water and make food from light — and phosphate feeds that growth. When too much algae accumulates, it can deplete the dissolved oxygen that fish need to breathe. This experiment fills eighteen jars with tap water and algae, then adds increasing amounts of a phosphate solution to most of them. Three jars get no phosphate and serve as the control. All jars go under a grow light, and dissolved oxygen levels get measured each day. The control jars hold the most oxygen, while jars with more phosphate generally show less — even small amounts make a measurable difference.

Phosphate feeds algae growth, and when algae thrive, they consume the dissolved oxygen that fish need to breathe. This experiment tests that relationship directly: eighteen jars of tap water each receive one milliliter of algae, then varying amounts of a phosphate solution. Control jars get none. All jars sit under a grow light while you measure dissolved oxygen daily with a dissolved oxygen meter. Jars with more phosphate generally ended up with less dissolved oxygen — even small amounts made a measurable difference.