Why is there no chlorine reading in my salt tub?

[mgulya]

So I have a Caldera spa that just hit 1 year in July, and I too have the Freshwater Salt system cartridge.
Here is what I have learned to make my life easier:
1. I ordered Phosphate test strips https://www.amazon.com/gp/product/B00MGKF32C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
2. Phosphate remover: https://www.amazon.com/gp/product/B00PZZFQRM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
3. when ever i get 1 0 reading of chlorine in my tub i test for phosphates and depending on the reading seems like once i hit 300 i lose chlorine, 1st I add 1 cup of liquid shock followed by the phosphate remover. 24 hrs later i retest and see where i am at. this keeps my water good for about 10 months.
cartridge issues i had 1 work for the 4 months and reach when the display said time to change it out.
every other cartridge somewhere in the 2-3 months will say low output levels. once i put a new one in everything works. My dealer says it is a chemical balance issue but i just got all my levels perfect and it still says low output.
has anyone figured out how to get 3-4 months with these cells. mine are all black with a grey little button and gray tabs on the side.