it is an 18 foot above ground. I put the soda in because a few years back we had the same proublem and after a test of the funky water, the local pool palace sold me a 10 lb tub of sada ash ( wich i did not know that was what it was as he would not educate me) I was told to put it all in and along with the shock, my pools christmas party was turning into clear water before my eyes..... I thought this year, it had to be the same, so i shocked and put in about 5 lbs of ash. Today, with lots of filter cleanings it seems a bit better, and the chorine reading is just in the" best" position. but not at shock level, so..... do I need more Chlorine? and the ph level is LOL believe it or not, in the " good position" ( i understand that you should not add soda until 24 hrs is up). dont want to over do this and turn this into a chemical bomb like i have done in the past, one i put so much shock in the pool, you could smell the chlorine three houses down. I now realize more is not always good. oh yes, the " shock i have is liquid chlorine the size of our pump is 1 horse power and a cartaridge filter. and i realy do not know what a CYA is....help and thanks! poolguy01