The other day I was servicing a Hot Tub, and when I added ph Increaser the water became cloudy. I'm wondering if anyone has any idea why this might happen. The Hot Tub has a nature 2 sanitizer, and I suppliment that regularly with Oxy Shock and granular chlorine. pH and Total Alkalinity are checked and adjusted weekly, and the filter is cleaned weekly. This was an instant reaction as soon as I put the pH increaser in, I could see the water clouding up.

I'm suspecting it could be related to hard water. Increasing pH could result in the precipitation of CaCO3. Is this the case, or is it something else?

Calcium precipitation was my first thought, or else the Nature 2's silver being knocked out of solution? Did you notice any color change along with the cloud? Do you know what the CH of the tub's water is?

A full set of water chemistry numbers, in particular the pH, TA CH, CYA and temp would let us calculate the saturation index. pH Up is calcium carbonate so increases pH, TA and CH and often clouds if the water is near saturation. It usually dissipates and clears up unless the water becomes too over-saturated.

I don't remember specific values, the best I can say is that TA was within the normal range, pH was a bit low because I had just added the oxy shock. Temperature was about 94. I'm not sure about CYA, we typically don't worry about it too much on hot tubs. CH was probably around 250, but I'm not totally sure.

But it sounds like my hypothesis about calcium is a reasonable possibility. I'm really just trying to get an idea what could be happening. Someone told me it could be bacteria, but I don't see why pH would cause clouding for bacteria. Like with most of my posts, I'm not trying to solve an individual problem, but trying to understand what is going on so I can think through other problems better in the future.

If the pH was 7.3 and the TA 100 ppm and CYA 30 ppm, then the saturation index with the rest of the numbers you gave would be around -0.1 so adding pH Up could certainly cloud the water temporarily by forming calcium carbonate locally until fully dispersed. We usually recommend a CH of 120-150 ppm which is enough to prevent foaming but helps prevent scaling since hot tubs have so much aeration that the pH tends to rise readily unless one uses acidic products (like the non-chlorine shock, MPS, that you used, or Dichlor which is net acidic when accounting for chlorine usage).