Hello, I have had my brs 4 stage 75 gpd since December and so it has been about 6 months. I’ve been using it more often than usual because I just set up a 60 gallon tank with live ocean rock and I’ve had to do big water changes. Now that I’m using it again today I’m noticing that the tds of the water coming in is 3 and the water coming out is 4. I’ve let it run for some time and it hasn’t changed. I just used it last week and tds was coming out as 0. I always make sure to flush the unit before and after use. Does this mean I have to replace the filters?