First of all hello everyone and thank you for all the information that is available on this forum. I am a relative beginner but learned a lot just from a little research. This may be a little long but I appreciate any help you can give me. A little background first. My family owns a RV Park and Cabins in Pigeon Forge, TN. We have been here 23 years and 12 years ago my dad installed a new 18,000 gallon in ground pool with what I call stucco sides but I'm sure it's called another term. The pool uses chlorine and has a sand filter. A couple years ago we started having problems with mustard algae growing when it rains or got really humid outside. We would scratch and carry on and nothing ever stopped it. We finally went to the company who built the pool and they recommended yellow out. We bought some and would shock it normally every week but it never really helped. It keeps coming back. This year we have finally had enough of spending money on this stuff because it has effectively quit working. I looked up on here what to do and first things first I purchased a tf-100 test kit. Here is my readings:
Total Alkalinity: 180
Calcium Hardness: 200
Based on these results I believe I have determined that our chlorine number is too low relative to our CYA causing our shock not to work and the algae to grow. Does this sound correct before I spend more time and effort on solving this problem? Keep in mind this pool is heavily used in direct sunlight in normally a very humid east Tn. Also, we have neglected our sand and probably need to change it out to fresh sand. Any suggestions to our problem as well as suggestions to keep our numbers normal?
Thank you very much everybody.