A few days ago I received my new new test kit from TFTestKits. Right away it was obvious that I need to replace a good amount of the water in my pool. My CYA measurement is 1/2" below the 100 mark. Since it looks like a logarithmic scale, I fear that the actual CYA significantly higher than 100. Also, my TA measurement is 380. As you can imagine I am having problems with both algae and scaling.
I know I have to drain the pool, but I'm not sure how much water to replace. It is a 20,000 gallon plaster/gunite pool. I live in Las Vegas and I am not too worried about my pool floating away if I drain too much water. Is it best to take all the water out and start over?
Now to the meat of my question. When the pool was being built I remember that one of the things I had to wait on was the sewer hookup. Since there doesn't seem to be anything to do with sewer drains around the pool equipment, is it possible that my plumbing is already connected to the sewer? All of my valves past the pump are accounted for and control things like spa/water feature/inground cleaner/solar heater. On the intake side, there is one path which is never used. I will attempt to attach a picture with 2 valves marked A and B. The A valve controls whether to pump the water from the spa or main pool skimmers. It is shown in the main pool position. The B valve is the one I never touch and currently pumping water from the main pool skimmers. My gut says that the sewer drain pipe is accessed with the other B valve position. However, my knowledge of fluid mechanics doesn't allow me to get my brain around how this could work. The other "unknown" pipe is a slightly smaller diameter than all of the other pipes. Am I completely off base?
I would rent a pump from home depot but I have looked around and I'm not sure where I would access the sewer drain directly. I would call the pool builder and ask them but they are no longer in business.
Thanks for any input you can give.