I have a 19k gallon pool with a tristar 2hp pump that runs for 3 hours at high speed and 9 hours at low speed. With this i have a Ultrapure UPP25 which requires me to set the SCHF (standard cubic feet per hour) air draw. The recommended SCHF is 5. if set at 4 or 5 in high speed its fine, but when it drops to low speed the SCHF drops to 1-2 due to lower suction. If i set at low speed then when it kicks up to high speed the pump will cavitate since its pulling in about 8 SCHF. How can this be resolved? Also, shouldnt the unit generate ozone anytime the pump is on? My pool builder had it wired so that it only generates on low speed.

Ignoring the fact that I don't think you should have an ozone system at all, there isn't any reason to have it running the entire time the pump is running. Because of the interaction with the pump speed, the way they originally had it setup makes the most sense. There isn't any simple way to have it work correctly at both pump speeds, so best to have it work at the pump speed that you use the longest (ie low speed).

My ozone injector overcomes this issue using a springloaded variable bypass checkvalve parallel to the venturi injector.

It is ideal to inject ozone last just before the water returns to the pool so the oxidation works on pool water and not your pool pump parts.

Some people inject ozone as a flocculent in front of their filters although I haven't tried this.

Just so you know, it takes a minimum of 24 grams of ozone per 4000 gal of pool water per day to oxidize most of the organic load. For this reason most people can only afford ozone for use in a smaller body of water such as a spa. And yes, that's a lot of ozone. And no, the ozone manufacturers will never tell you this.

Good luck,

Lee

As a point of reference, in a spa, one person-hour of soaking at 100-104F takes around 5 fluid ounces of 6% bleach to handle the load and this is about 10 grams of chlorine which is equivalent to around 7 grams of ozone. The load from swimming in a pool for the same person-hour is probably around half this amount (one sweats a lot less). So unless the ozone is being used up by a lot of organic load that isn't sweat/urine or is otherwise broken down by other means or lost in inefficiency, the 24 grams seems high and wouldn't be scaling with volume of water anyway. For a 350 gallon spa, that would be about 2 grams which seems too low.

Losses from breakdown from sunlight or other losses not related to bather load itself would be proportional to volume of water, but oxidizer usage from bather load depends only on that bather load independent of water volume. Load from dropped in organics would probably be proportional to the surface area of the pool.

Plumbing a suction side Ozone system into a multispeed pump is done different ways by different pool builders. If you can get a draw on low speed as well as high speed, the unit should be wired to light on both speeds. The set air draw can be a little deceiving, more is not always better. As long as you have a visible air draw you are getting Ozone into the system. Each of our units manufactures a specific amount of Ozone, the lower the air draw is set, the higher the concentration of Ozone to ambient air is. There are some pumps on the market that will simply not draw hard enough to open the check valve when running on low speed, in these cases we recommend that the system be wired to high speed only so as not to waste the lamp life of the UV bulbs.

Additional points that were off topic for this thread have been moved here. JasonLion