Often times this means that your Ozone Purification System has expired. Just like with your town's water, without a functioning ozone system, more chlorine is needed. Like theirs, your Hot Tub's system has a limited lifespan. 

You may also need to replace your Silver Ion (Ag+) Cartridge if it's been more than 4 months. The Ag+ cartidge works together with the ozone system to keep your water crystal clear, reducing the need for chemical additives.