Chlorine being eaten up ?

[ducru]

Hello. We are now in the deep freeze in Eastern Canada, and I seem to be having sanitizer issues.  We use lithium as a sanitizer and I have never had any problems keeping the levels up.  Now, for the past week or so, levels seem to be falling off very/too quickly.  I am adding 1 TBSP of lithium per bather, after soaking (as I always have), but by the following morning, there is nothing left when tested.  Also, the water is looking a little cloudy, though it smells OK­.  All this seems to coincide with New Years Eve (celebrated by 8 people in the spa) but also with the opening of a new pail of lithium. It was a tame celebration on New Years Eve, consisting of a total of 2-3 soaks, with 3-6 persons in the spa at a time, some sipping their Champagne.  I have no doubt that this affected the water, but I did add the same 4 tbsps I normally add to shock the water and assumed that all would be OK. Now, when I test with a strip, there is rarely any discernable level of sanitizer left in the spa. In fact, yesterday, I tried adding 2 TBSP of lithium, though no one had used the spa, waited an hour and retested. After 1 hour, the level was at 3-4 PPM; much lower than what I would have expected (FYI it's a 350 gallon spa).    Is it possible the new bucket of lithium is faulty ?  It's not the same brand as I was using before, but shows the same concentration levels on the label.  All other levels are stable: Alk: 50-55 ppm, ph: 7.4 ppm and  CH: 220 ppm. Any ideas on how I can gain the upper hand ?

[hottubdan]

How old is the water?

[ducru]

The water was changed at the end of November.  I haven't checked recently, but as of mid-December, TDS was at 6250.

[Sam]

The heavy bather load (new years) created a larger chlorine demand.  You need to add more chlorine to meet that demand.  Try shocking it again.  It may take a couple of doses.

[Kev B]

 High phosphate levels may be the issue. Phosphates eat up chemicals quickly and sometimes come in through the fresh water from the city, shampoo, soaps,clothing, etc.....get a phosphate test kit and if they are high, there is a product to remove phosphates....the product coagulates them and makes your filter pick it up so the filter (s) will need cleaned the next day.

[chem geek]

Except for very high calcium and phosphate levels that can precipitate calcium phosphate, phosphates do NOT eat up chemicals quickly.  Phosphates and nitrates are essential nutrients for algae growth so in water exposed to light such as swimming pools higher phosphate level can lead to apparent higher chlorine demand from the algae growth IF the Free Chlorine (FC) level is not high enough relative to the Cyanuric Acid (CYA) level.  If the FC/CYA level is high enough, then the active chlorine kills algae faster than it can grow regardless of algae nutrient (phosphate and nitrate) levels.

2-3 soaks of 3-6 people is a huge bather load.  If the soaks were even 30 minutes, then that would be 3 to 9 person-hours of soaking.  Every person-hour of soaking in a hot (104ºF) spa with no ozonator requires roughly 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS) or 5-1/2 teaspoons (nearly 2 tablespoons) of lithium hypochlorite.  Your 4 tbsp of lithium hypochlorite would be enough to handle (4 tbsp)*(3 tsp/tbsp)/(5.5 tsp/person-hour) = 2.2 person-hours and your additional 2 tbsp would handle 1.1 person-hours so a cumulative total of 3.3 person-hours so not enough to handle the bather-load.

Sam's advice is spot on.  You just need to add more chlorine to meet the demand.