Turn Over Rate
Also called turnover rate - The period of time (usually in hours) required to circulate a volume of water equal to the volume of water contained in the spa. Spa capacity in gallons, divided by pump flow rate through the filter in gallons per minute (gpm), divided by 60 minutes in 1 hours, will give turnover rate.
Commercial spa must turn over once every 15 to 18 minutes to ensure proper sanitation and clarity
The rate at which the water is travelling through the filter, expressed in U.S. gallons per minute (gpm) per square foot of filter area. The filter as it becomes filled with debris will allow less water to pass through the material and a lower turn over rate will be a result.
A Filter bypass will not solve this dirt filter problem because the bypass allows the water to miss the filter and the debris now ends up back in the spa and interferes with sanitation and its ability to kill the algae and bacteria.
Total Dissolved Solids (TDS)
Total dissolved solids (TDS) is a measure of how "tired" or well used the water has become more accurately it is also a measure of how many salts are in the water. As more chemicals are added, the higher the TDS level. High TDS levels indicates that a partial draining and addition of fresh water (of a lower TDS value or level) is required to reduce the continued high readings. All other factors being equal, high TDS in water have an increased tendency for the water to cause corrosion even at pH levels that are ideal. Most pools/spa water has a TDS less than 2000 ppm, which has little effect on water balance. As spa water in particular ages and chemicals are continually added, the TDS does become a factor, hence the reason spas need to be drained frequently. The more you use your tub, the more chemicals that are required and the more frequently the water should be drained and refilled or at least diluted. Also as the TDS build up in the water they can displace the calcium hardness in the water slowly making the water soft.