- 1 OTO and 1 phenol refill. 2 x botlle 15 cm3 each - 5 sets
- OTO is a solution that turns yellow when added to chlorinated water. The darker it turns, the more chlorine is in the water.
- Phenol Red The pH test is a fairly straightforward one. It is based on phenol red solution which turns different colors based on the pH of the water.