It's muriatic. I would add chlorine only at start up & acid only when it's needed. Your supplier can show you how to check the pH & determine when one or the other is needed.
Should chlorine tablets be used in place of stabilizer chlorine tablets so the cyanuric acid don't get to high?
Chlorine is effected by sun, air, temp and bather load. You should check first to see that your stabalizer (cyanuric acid) level is ok, 30-50 ppm. That will help chlorine stay in water.
Use stabilized chlorine only so long as stabilizer level (cyanuric acid level) in pool is within the recommended range of 50-80ppm.
Assuming no other complaints you would only need to change water to lower the total dissolved solids level or cyanuric acid level. TDS should be below 500ppm and cyanuric acid ~50 ppm.
Chlorine level in an 18' above ground pool should be between 2 and 4.
manual
If you are getting a low reading of chlorine in your above ground pool, you should add the appropriate amount of chlorine to get it back to the correct level. This is important to keep your pool running at maximum abilities.
Chlorine is taken up by biomaterials for one. that is the more dirt there is in the pool even stuff you cant see the more chlorine seems to disapear. the sun and the activitys of swimmers also have a big effect on chlorine consumotion. to hold onto the chlorine longer, Conditioner or Cyanuric Acid Levels should be kept up to about 80ppm, Low conditioner levels will lead to a lot of the chlorine in the water being burned of without it being utilized.
The constant use of small 1" , large 3" jumbo chlorine tabs and granular chlorine. they all have cyanurics acid in the compound mix. Best to switch to liquid for a while ( a month of so). The high levels of cyanurics will eventually drop as water evaporates and you add fill water. High levels of cyanuric acid or conditioner would be considered to be in excess of 100 ppm. You could also do a partial drain of the pool and refill to reduce the CYA faster. In the future you might consider alternating between liquid 12% chlorine and tabs. Note: 1" tabs dissolve faster. HTH granular and tabs I believe do not contain conditioner but then it is a lesser grade of chlorine - see percentage values on label.
Manual Startup. Use services.msc in command prompt to set the startup.
I cant see why it should be drained and given a chlorine bath at all. If there is no problem with the water or the looks of the pool leave it alone.
A reasonably healthy pool should have nothing in the water but chlorine or other sanitizer to sanitize it cyanuric acid to stabilize the chlorine salt if its a saltwater pool sometimes there may be algaecide there as well, muriatic acid, calcium , some dust, oils. body-fats and a few other impurity's.