Hello and welcome to TFP! We probably should be cautious about your situation since your thread title addresses not only concerns for dirt, but then you also appear to describe calcium/scale. Definitely different approaches to each. And while lowering pH for a while can help to remove scale, my biggest concern is trying to relate that to dirt that appears to be adhering to the bottom. Also keep in mind that to try and remove scale chemically, you have to be careful about just setting an arbitrary pH number since you really need to adjust the CSI index more than anything, and that is driven by all three (pH, TA, and CH).
It might be best for you to post a full set of numbers for us (with your TF-100 or Taylor K-2006) to evaluate before dropping your pH. We may gain more insight that way. Also, please add your pool info to your signature by going to the top of the TFP web page (just under the Pool School button) and select "SETTINGS". On the next page look to the left for a menu bar that says, “MY SETTINGS” and go to "EDIT SIGNATURE" to enter your pool and equipment info there. It will help us later.
We'll watch for yoru reply and do the best we can to advise. Nice to have you with us!