Should I be taking the pump apart and cleaning it already?
That's very unlikely. Most pools go years without clumping, if they ever do. Infact, many of us on the forum
never change the sand. You will find many folks with sand 10+ years old.
The reason yours clumped and got hard was improper chemical balance and allowed dead algae, perhaps calcium (not likely) or something else to accumulate without it being backwashed out.
It would not be a bad idea to remove the lid from you filter and inspect the sand to reassure yourself. You will likely find some gunk around the top and it may be just a little bit crusty but you should not have to change it.
Your continued overnite FC loss is very puzzling to me. Do you have entrance steps or anyplace else where algae might hide. Removing the ladder was a good idea but, even with what you found on it, I don't think it would account for the FC loss you are experienceing.
I understand what teapot was suggesting. He/she was eliminating the filter as a source of the FC loss. That's not a bad idea but I think it would be as easy to remove the lid and visually inspect. I don't think any algae in the filter could survive your constant barrage of high FC but I am puzzled as to the source.
Are you observing you filter psi? With that much FC loss, the dead organics should be causing your filter pressure to rise. What has been your backwashing history during this 17 day period?
After you post back, I've got some more questions but let me say this good news.........The constant level of high FC will work. It has worked on every pool on this forum for years and it will work on yours. You must stay the course and your pool will get clear. I am convinced we can figure out the chlorine loss and solve it but, in the meantime, it is essential that you stay the course and continue to keep your FC up in the 20ppm range like you have been doing.