Hi there. I've been reading, and reading, and reading the forum questions and answers and feel like I'm in waaay over my head. So, let me apologize for asking the same questions that have already been asked and answered numerous times. But hey, I guess that's what a forum is all about.

We have an inground, 21,000 gal. pool with a sand filter and vinyl liner.

We've been battling keeping chlorine in the pool all season (opened mid-May). Last week, the clear water went cloudy. We took a water sample to the pool company, and they asked when the last time our sand in the filter had been changed. We didn't know, so we scheduled them to come out and change the sand. They told us we had "trace amounts" of phosphates, and that they were eating up all the chlorine. Our pH was also low, so they told us to add 20 lbs of baking soda. They also said to add a couple pounds of shock to the pool, and that they would be out on Thursday, the 1st to change the sand. They said to just add enough chlorine to the pool to keep it from going green, and that changing the sand would fix the problem of our chlorine being hard to keep up.

Sunday evening, the water started getting darker. Monday it was green. We added 4 lbs of shock Monday night. This morning, it looks even darker green. We can't see the bottom of the deep end now. I took in a water sample and here were the readings:

TDS: 500
CYA: 86
Total Chlorine: 1.5
Free Chlorine: .4
pH: 7.3
Total Alkalinity: 217
Adj. Total Alk: 191
Total Hardness: 190
Copper: 0
Iron: 0
Manganese: No

After reading some of the posts, I'm inclined to add more shock tonight to try and get the water clearer. However, I'm concerned to do that, because the pool people said it was just wasting chemicals until after the sand is changed.

Any help and advice would be greatly appreciated. If you need further information, please let me know. Thanks!!