TDS is not a professional way to test the water quality, TDS means total dissolved solids. For example, if you put very little salt(NaCl) into the water and test the TDS, you will find the result is dramatically high. The same thing, if your water is full of minerals, the TDS is very high too.
The SK99 doesn’t remove any of the minerals from water, it only stops heavy metals such as Lead, Mercury, Cadmium, and over 70–80 VOCs, and it removes greatly the chlorine from water. Therefore, it is the reason why the TDS you get is not that lower as you expect.
TDS meter testing method is widely used in reverse osmosis systems since the RO filter system also removes minerals from water. If a RO membrane doesn’t have a good performance, the TDS will be relatively high. And if TDS is getting much higher, means it’s time to change the RO membrane.
So please do not use TDS to test any water except Reverse Osmosis System, because the result is meaningless.

About the service life of the FZ-2 filter cartridge for MK99, there is no exact time to tell customers when to change the filter, all the specification data of the flow capacity that is listed on the sticker is based on actual test from the laboratory and it's provided water. The feed water quality is very much different for different users. If we have to give out a service life by time, we would say 6–8 months based on your water quality and the volume of water you use every day.
Here are some suggestions to judge if it's time to change the filter: First is the taste, if you feel the taste of the water has a big difference, then it's time to change. Second is the water flow, the carbon has the highest precision of 0.5 microns, 10 times higher than most of the other brands with a similar product, if your water is getting too bad, it means the carbon is blocked because your water has many small particles and VOCs.
You will need to know that the performance of a water filter is decreasing by daily usage and will finally get exhausted, so Frizzlife will suggest every user change the filter more often to get the best water.

This filter should be used in conjunction with municipally treated drinking water or water that has been properly disinfected before use. The water filter cartridge is manufactured with 0.5 micron carbon (top rate) that will get easily clogged up by any type of dirt or sediment from a well.

If you would like your refrigerator or ice maker to have clean and safe water from the Frizzlife filter system, we also have an IMC-2 icemaker kit available on our online store.