Just heard about this web site. The company who tests my pool water says I have a high concentration of nitrates and I have been shocking the pool daily for the last week. Still can't keep free chlorine level up. I test the water right after the shock and it already shows no free chlorine. I've been using test strips but now see there is a better testing kit out there, how do I get one of these? I have an in ground pool, vinyl liner, 16X32. I've had the pool for over 20 years and never this problem until the last two years. Really need help!