You need good Salt, Cya, and pH for the system to maintain a good residual. However, there are other parameters that are important too. Maintaining your water to ensure water chemistry balance, according to the Saturation Index, will ensure that your cell is scale free. These parameters include Total Alkalininty and Calcium Hardness (along with pH and water temp).
Cya is important for protecting the chlorine from degradation of the Sun's UV.

Get your water retested for salinity to ensure that you are around 3000 ppm.

The funky smell is usually due to high combined chlorine levels or stagnant water.
Cloudiness is usually due to chlorination and/or filtration, or a combination of high pH, total alkalinity and calcium Hardness levels.

As your system is about 4 yrs old, you may want to consider replacing the cell. They typically last 3 - 5 years.