Hi Taraka:
Tony's right on the mark about chemistry, unless you are a "heavy" user. The purpose of Ozone and Nature2 is to reduce but NOT eliminate the amount of chemicals added to the water, making the water "smoother" for use. Like you, I use both an Ozonator and Nature2, with 2 ppm being a good "base" level for chlorination.
The test strip you are using probably has 2 "chlorine" readings, "actual" and "free" (sometimes called "residual"). Your readings should be at the "minimal" levels on the strip. BUT, be careful. New tub owners sometimes get complacent about chemistry and don't realize that sanitized water doesn’t necessarily mean "clean" water. Dirt suspended in water makes it foam and get cloudy. Only FILTRATION and other treatments get rid of dirt.
"FREE" chlorine also comes into play when you suddenly increase tub usage by a number of people. Say only you and someone else use your tub on a regular basis. You "minimally" treat your water as we have discussed and the water chemistry is in "equilibrium" for your level of use. On Saturday night, you have a bunch of friends over for a “hot tub social.” You add the dichlor after the party as indicated but Sunday when you go to use the tub, the water looks like crap.
Two things most likely happened. The first is that the FREE level of chlorine probably wasn't high enough to take care of sanitation BEFORE a problem occurred. Nature2 is a great product, but it doesn’t respond quickly to changing water situations. Consider pre-shocking the tub about 2 to 6 hours before heavy use if you know it's coming -- ESPECIALLY if kids will use it.
The second problem is that "dissolved solids," stuff like body oils, fats, lotions, deodorants, etc., end up "clouding" the water. This happens when a bunch of people use the tub, even if they take showers before getting in. Unless the sanitizing additive you are using includes a "clarifier," the water will still be dirty, even if chlorine levels are "OK." Switch to a vinyl pool shock containing dichlor with added “clarifying” agents and start using a product like "Super Clear Clarifier" by AquaEZ (see my recent post in the “What color should water be?” thread).
Good luck and hope this helps...
Drewski