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for some reason I thought there was a test or something. So it sound to me like if the tub is 4 years old time to replace it.
Ozonators come in many different varieties and qualities. Some will last 5-10 years, others much less. Some CD ozonators need a chip replaced yearly, others never in the life of the unit. There are UV ozonators that need a bulb replaced periodically and there are solid state UV ozonators that are a higher quality.It is difficult and expensive to test for ozone and maybe practically impossible in a spa because of the very small amount introduced to the water in relation to the volume of water.The yellow substance is nitric acid produced from your ozonator.
Vinny - What brand of spa do you have and what type of ozone were you using?
There is a spa ozone detector sold. Just do a Google search for "spa ozone detector". It's got a picture of a dog on the packaging. Never used it so I can't attest to its efficacy.
Well i can tell you that when you bought your Cayman you had 2 options for an ozone system. One was a UV and the other (which also cost more) was a CD ozone. That could explain some of your issues given that it used a fairly "cheap" ozone for their UV models. BTW is your spa running on the 24hr Grunfros circulation system with the Laing Heater or are you using the 2 speed 4hp with Stainless steel heater?I ask because you tend to have better results with the 24hrcirc pump rather than their 2 spd system. You really shouldn't get cloudy water after 3 days in any spa provided that your chems are in balance and you didnt bring your dog in the spa