Water Balancers: To keep your water in balance, you should test the pool several times per week for chlorine and pH levels, and adjust as needed. Test total alkalinity every few weeks or if you have pH troubles, and test calcium hardness and cyanuric acid levels every month. pH Increaser: Granular Soda Ash.
The alveoli are surrounded by tiny blood vessels, called capillaries. The alveoli and capillaries both have very thin walls, which allow the oxygen to pass from the alveoli to the blood. The capillaries then connect to larger blood vessels, called veins, which bring the oxygenated blood from the lungs to the heart.
This is where gas exchange takes place in the lungs. Alveoli are tiny balloon-like sacs, in the lungs, where gas exchange takes place and they serve as the barrier between the external environment (the air) and the internal environment (the blood).