I am having customers coming in with high levels of Combined. I treated one customer, 30,000 Free was .66 and total was about 6.5, ph was 8.2, TA was 140, and CYA was around 23.
I had him add some Acid to the pool, then shock with roughly 18lb of Cal Hypo, he came in a few days later with these readings.
F- .6
T-4.6
CC-4.0
PH-7.9
TA-95
CYA-20
What else can you do with high levels of Combined?
The pool was greenish, now it is just cloudy,
Phosphate was below 500 and no metals, no high levels of TDS either.
Replies
Chlorine and Oxone (MPS) are both selective oxidizers. When one opens a pool with bacterial conversion of CYA into ammonia, then either one will equally oxidize ammonia as well as the CYA fragments. So in that case, the 2-3x difference in price would normally be the deciding factor.
It's only when you have more usual CC situations in active pools with higher bather load where Oxone can sometimes do a better job than chlorine, especially if used in maintenance mode where it can oxidize some organics (and ammonia) before chlorine gets a chance so it can reduce disinfection by-products. Some commercial/public indoor pools use Oxone for this purpose -- to reduce disinfection by-product formation.
For homeowners, there are articles at Trouble Free Pool (TFP) in the Pool School including Defeating Algae, Shocking Your Pool, and Turning Your Green Swamp Back into a Sparkling Oasis. However, these focus on using physical removal, filtration, and shocking with chlorine which takes longer but is the least expensive approach. For you guys who don't have a lot of time, you'll want to use additional products at extra cost as you've seen here at PGN such as Proteam System Support (to raise leaves up from the bottom) and will want to use clarifiers or flocculants to clear water faster.
The specific problem of opening to a huge chlorine demand from bacterial conversion of CYA into ammonia is less common so there's not an article specifically on that except the technical one I linked to earlier. Basically, you just keep adding chlorine frequently until you get an FC reading that holds consistently. There's no way around it. You can use more expensive oxidizers like MPS, but it doesn't make things go any faster. When this happened to me, I caught it during its conversion and hit it hard to try and stop it. It's amazingly fast since the pool was with zero chlorine for perhaps just 3 days. You can inhibit the process by using phosphate removers to keep phosphate levels low as a preventative since that will slow down (though not stop) bacterial growth. The best preventative is always keeping a residual chlorine level, but of course that's not normally done in pools that are closed (winterized) where the pump is turned off and the water usually freezes over. Shocking the pool before closing and using PolyQuat 60 can also help, but the key is to close and open the pool when the water is still cold (< 50ºF), if possible.
Some pools lose their CYA over the winter but don't open up to huge chlorine demand. In such cases, I figure the ammonia either partly outgassed or got taken up by algae (if the pool has algae upon opening). There are some pools where the CYA goes away but open up clear without chlorine demand and though ammonia could have outgassed, it seems unlikely to be that much so that's still a mystery I haven't figured out (yes, water dilution would cut down CYA some, but not completely as is often seen).
One does not need 10x chlorine levels to "break" for breakpoint chlorination. The oxidation of chloramines is continuous so long as an oxidizer is added. The MPS and chlorine will both oxidize, but the MPS is more expensive than chlorine. The amount of oxidizer needed is not 10x because the CC measurement is in chlorine (ppm Cl2) units, not ammonia (ppm N) units and one of the 1.5 needed chlorine is already part of CC.
Anyway, since 18 pounds of 65% Cal-Hypo in 30,000 gallons is 46 ppm FC and the CC only dropped a little and you still aren't measuring much FC, I suspect you had a lot of ammonia in the water, probably from bacterial conversion of CYA into ammonia. When pools are "let go" over the winter and the chlorine levels go to zero, bacteria can convert CYA into ammonia which creates a huge chlorine (oxidizer) demand upon spring opening. Technical details about this are in Degradation of Cyanuric Acid (CYA) while my own personal experience with this is described in It Can Happen to Anyone - Zero Chlorine, CYA --> Ammonia. Note that it can take more chlorine or other oxidizer than would be indicated by either the ammonia or the CC level because there may be partially oxidized CYA chemicals that do not register in any of the standard tests. If you know how much the CYA dropped over the winter, then the upper limit is that every 10 ppm CYA lost will require up to 30 ppm FC cumulatively added to get rid of the resulting degradation products.
In the example you gave, you need to just continue to add acid to get the pH down and then more chlorine, unless you want to spend more and use MPS instead. I suspect you are more than halfway there for this pool, maybe even close to the end if you add chlorine and measure FC within 10 minutes or so (chlorine combines with ammonia VERY quickly to form monochloramine that shows up as CC, not FC).
If you have other pools coming in from spring opening, then in addition to FC and CC tests, you can do an ammonia test. Monochloramine will measure in both CC and ammonia tests with 1 ppm ammonia measuring as 5 ppm CC so subtract 1/5th the CC measurement from the ammonia measurement to know the actual amount of ammonia. The 10x rule you referred to earlier applies to ammonia so if you measure say 3 ppm ammonia then it will take about 30 ppm FC cumulatively added to oxidize it. But that's a minimum as I noted earlier because of some additional partially oxidized CYA that won't show up in any tests. You don't have to raise the FC to add it all it once -- just keep adding it as soon as the FC level drops, which initially will be every hour or so (see how quickly and how much chlorine I needed to add in my own pool in this post).
We use Monopersulfate to shock our pools.
Breakpoint chlorination is so high with a 6.5 TC (roughly 6.0 CC) reading that it will take a crazy amount of Cal Hypo to "break"...
Potassium Monopersulfate will break down CC without having to add crazy amounts of chlorine to the water.
All of my service trucks keep a 50# pail with them at all times... we add about 1# to pools as needed (which ends up being every 3 - 5 weeks usually).
I suspect that the water is now cloudy because you added so much calcium to it... It is one of the reasons why I do not like Cal-Hypo and we do not use it at all...