Tested this evening at 0.8 ppm FC, 0.2 ppm CC.

I added 16 oz of cal-hypo again, and this time I noticed that the water coming out of the outlet was cloudy. I'm guessing that's the blow-through, and I'll need to replace the filter sand. With the pipe cutting required, and the advantage of installing unions as was previously mentioned, I'm thinking I'll probably hire this job out.